0:00:02 > 0:00:04This is the Britain we know.
0:00:04 > 0:00:11A patchwork of fields, forests, of rugged mountains,
0:00:11 > 0:00:14and dramatic skylines.
0:00:14 > 0:00:18But ours is also a land of secrets that you can only see
0:00:18 > 0:00:19if you look at it in a new way.
0:00:23 > 0:00:25From beneath.
0:00:25 > 0:00:29I'm going to show you Britain as you've never seen it before.
0:00:31 > 0:00:35A hidden, vibrant world that we rely on every day to keep
0:00:35 > 0:00:37the country moving.
0:00:40 > 0:00:43Bustling with life, unseen beneath our feet.
0:00:48 > 0:00:51I'm going to explore the secret superhighways we've created
0:00:51 > 0:00:53over 200 years.
0:00:56 > 0:01:00Whichever way you look at it, this is a marvel of engineering,
0:01:00 > 0:01:02even by modern standards.
0:01:03 > 0:01:06I'll see how London's newest railway
0:01:06 > 0:01:09is forging its way beneath the streets.
0:01:10 > 0:01:13The accuracy of all of this is stunning as well,
0:01:13 > 0:01:16it's millimetre precision.
0:01:16 > 0:01:19And how some of the most magical parts of our country
0:01:19 > 0:01:21are deep below the ground.
0:01:21 > 0:01:25That was amazing. Really amazing.
0:01:25 > 0:01:30I'm going to discover how everything that we see in our thriving, vibrant
0:01:30 > 0:01:35Britain can only really function because of what we can't see.
0:01:35 > 0:01:39A secret world of networks, of connections that are hidden
0:01:39 > 0:01:40underground.
0:01:51 > 0:01:55I'm starting at Heathrow. The busiest airport in Europe.
0:01:55 > 0:01:59But this is an airport with a secret.
0:01:59 > 0:02:01One you wouldn't guess from the familiar hectic
0:02:01 > 0:02:03world of the terminal.
0:02:05 > 0:02:06There's another world,
0:02:06 > 0:02:10invisible to the eye, that's key to getting you into the air.
0:02:12 > 0:02:1572 million people came through here last year,
0:02:15 > 0:02:18which works out at nearly half a million flights.
0:02:20 > 0:02:23Every one of those flights needs fuel.
0:02:23 > 0:02:27We burn through nearly 14 billion litres of aviation fuel a year.
0:02:32 > 0:02:37If all that fuel were carried on the roads, then the petrol tankers
0:02:37 > 0:02:41would clog up the entire British motorway network,
0:02:41 > 0:02:45which makes you think, where is all that extra traffic?
0:02:45 > 0:02:49The answer lies in a secret world underground,
0:02:49 > 0:02:53that came into existence during Britain's darkest days.
0:02:53 > 0:02:55AIR RAID SIREN
0:02:55 > 0:02:59It all began in World War II with the Battle of Britain.
0:03:01 > 0:03:04The nation's survival depended on the RAF defeating
0:03:04 > 0:03:06the German Luftwaffe.
0:03:10 > 0:03:13So, it was crucial to keep our planes in the air.
0:03:17 > 0:03:20Now, if an army marches on its stomach,
0:03:20 > 0:03:23then a plane flies on its fuel tank.
0:03:23 > 0:03:27And a new breed of fighter aircraft that were designed to protect
0:03:27 > 0:03:30Britain in the Second World War, like the Spitfire or the Hurricane,
0:03:30 > 0:03:35were incredibly thirsty beasts. In fact, the future of the nation
0:03:35 > 0:03:39really did depend on being able to get enough fuel to these planes.
0:03:41 > 0:03:44Fuel was too precious to keep above ground,
0:03:44 > 0:03:47where a well aimed bomb could blow it up.
0:03:50 > 0:03:53So, the RAF began to do something clever to keep fuel
0:03:53 > 0:03:55out of harm's way.
0:03:56 > 0:03:57I think this might be fun.
0:04:03 > 0:04:04Up we go.
0:04:06 > 0:04:09As we fly over the Wiltshire countryside, I'm going
0:04:09 > 0:04:13to try to spot it from this original World War II reconnaissance plane.
0:04:16 > 0:04:17Oh, what a great view.
0:04:24 > 0:04:27They made sure it was well hidden.
0:04:27 > 0:04:29In fact, so well hidden, it's hard to find.
0:04:34 > 0:04:38OK, so, there it is, you can just see it, the Micheldever Fuel Depot.
0:04:38 > 0:04:40It doesn't really look like much at all, you can
0:04:40 > 0:04:42just see these two ridges.
0:04:42 > 0:04:46There's actually a whole load of fuel tanks buried underneath there,
0:04:46 > 0:04:51concealing the important aviation fuel.
0:04:56 > 0:04:59As more fuel was needed, more underground fuel stores
0:04:59 > 0:05:01like Micheldever were being built,
0:05:01 > 0:05:04but there was another problem, because there were only two
0:05:04 > 0:05:08sea ports that could distribute the fuel to the various stores -
0:05:08 > 0:05:12Avonmouth in the south and Merseyside in the north.
0:05:13 > 0:05:17From there, all fuel had to be transported by lorry,
0:05:17 > 0:05:19making it vulnerable to attack.
0:05:21 > 0:05:24So, in 1941, the RAF hatched an even more
0:05:24 > 0:05:26ambitious plan,
0:05:26 > 0:05:29which was to send all that fuel underground.
0:05:35 > 0:05:38It began simply enough, with an underground pipeline joining
0:05:38 > 0:05:40Merseyside to Avonmouth.
0:05:41 > 0:05:45North and south were now connected, but fuel was needed
0:05:45 > 0:05:46in airfields in the east,
0:05:46 > 0:05:50so working secretly at night, engineers extended
0:05:50 > 0:05:54the underground fuel network to Kent, East Anglia and Lincolnshire.
0:05:56 > 0:05:59The pipeline now criss-crossed the country,
0:05:59 > 0:06:02delivering fuel without ever going near the surface.
0:06:06 > 0:06:11This was the GPSS, or Government Pipeline and Storage System.
0:06:14 > 0:06:18We're actually flying right along one of the pipelines now, but of
0:06:18 > 0:06:21course you'd never know flying above here. Completely buried, there's
0:06:21 > 0:06:24absolutely no evidence at all, which is exactly what the British wanted.
0:06:29 > 0:06:33The pipeline remained secret throughout the war.
0:06:33 > 0:06:35It kept our air force flying
0:06:35 > 0:06:37and helped turn the tide in the allies' favour.
0:06:44 > 0:06:47And remarkably, we still need this same pipeline to get us
0:06:47 > 0:06:49into the air today.
0:06:52 > 0:06:55This is how Heathrow Terminal Five looks from below.
0:06:58 > 0:07:01Once an RAF base, it's now one of the busiest
0:07:01 > 0:07:06airports in the world. 1,200 aircraft use it every day.
0:07:07 > 0:07:09All this is only possible
0:07:09 > 0:07:13thanks to the intricate system of fuel pipes hidden underground.
0:07:17 > 0:07:21Each pipe delivers fuel from right across the country,
0:07:21 > 0:07:23direct to a plane at its stand.
0:07:26 > 0:07:33Beyond Heathrow, Manchester, Gatwick and Stansted are all also connected.
0:07:33 > 0:07:37In fact, half of all the aviation fuel used passes through
0:07:37 > 0:07:41a direct descendent of the old wartime pipelines.
0:07:42 > 0:07:46It's extraordinary to think that the underground network that gets us
0:07:46 > 0:07:50on holiday today is the same one which helped us win the war.
0:07:59 > 0:08:02As a nation, we're always on the move.
0:08:03 > 0:08:06We make more journeys than ever before.
0:08:07 > 0:08:10This pushes engineering to the limit.
0:08:12 > 0:08:16And there's a place in Britain where, over the last two centuries,
0:08:16 > 0:08:18this has played out in a spectacular way.
0:08:22 > 0:08:26These are the huge bridges that span the Firth of Forth, connecting
0:08:26 > 0:08:29the Highlands of Scotland to the rest of the country.
0:08:34 > 0:08:38But the secret that makes all this possible is deep beneath the seabed.
0:08:45 > 0:08:48Before it was built, the only way to cross the Firth of Forth was
0:08:48 > 0:08:51to head up to Stirling, which is that way, which is going to add
0:08:51 > 0:08:56another 60-odd miles to your journey, or do what I'm doing.
0:08:57 > 0:09:01Neither of which are ideal. Not what you'd expect
0:09:01 > 0:09:03from a connected country.
0:09:06 > 0:09:08So, in the 1880s,
0:09:08 > 0:09:11Victorian engineers decided to build a bridge.
0:09:13 > 0:09:18It is such a familiar landmark, it's almost impossible to
0:09:18 > 0:09:21imagine just how radical it was when it was built,
0:09:21 > 0:09:23but the world had seen nothing like it.
0:09:28 > 0:09:32The Forth Rail Bridge was the biggest bridge in the world
0:09:32 > 0:09:35and the first made entirely from steel.
0:09:35 > 0:09:3855,000 tonnes of it.
0:09:38 > 0:09:42More than 4,500 men worked on it for eight years.
0:09:49 > 0:09:52I'll tell you what, actually being this close,
0:09:52 > 0:09:56you get a view of the bridge that you never normally get
0:09:56 > 0:10:00and suddenly it becomes a completely different structure almost.
0:10:00 > 0:10:04You can actually get really, really close and see the rivets themselves.
0:10:04 > 0:10:07You can actually see how the whole thing is put together.
0:10:10 > 0:10:13Obviously it takes some pretty spectacular engineering to build
0:10:13 > 0:10:17something like this, particularly at the time it was built, but
0:10:17 > 0:10:20just for a moment, ignore all that majestic metal work above us
0:10:20 > 0:10:25and just concentrate on these piles, because the real genius
0:10:25 > 0:10:29of this bridge is what's going on here, actually beneath the water.
0:10:34 > 0:10:37So, to really appreciate what made the bridge such an engineering
0:10:37 > 0:10:42triumph, we need to view it from deep below the waves.
0:10:42 > 0:10:44Seen from this perspective,
0:10:44 > 0:10:47the foundations take on a whole new prominence.
0:10:48 > 0:10:53Great stones piles stretch nearly 30 metres below the water,
0:10:53 > 0:10:56anchoring the bridge to the seabed.
0:10:56 > 0:11:00Building them was a massive engineering challenge.
0:11:02 > 0:11:05Foundations for a structure this size would be
0:11:05 > 0:11:06tricky enough on land.
0:11:07 > 0:11:11Underwater takes the problem to a whole new level.
0:11:14 > 0:11:19What they did was lower huge metal cylinders or caissons to the seabed.
0:11:22 > 0:11:27I've got a copy of the original plans made of the caissons
0:11:27 > 0:11:29and they're fascinating.
0:11:29 > 0:11:31They really capture how they work.
0:11:35 > 0:11:38So, once the caisson is actually put in place and weighed down,
0:11:38 > 0:11:42what you then have to do is pump all that water out using compressed air.
0:11:42 > 0:11:44And this is the clever bit here. You create this
0:11:44 > 0:11:49gap at the bottom, about 70 feet below the surface, and the men
0:11:49 > 0:11:54would actually work here in the most horrifically dangerous conditions,
0:11:54 > 0:11:59actually building the foundation and anchoring the bridge to the seabed.
0:12:03 > 0:12:05It's a brilliant solution
0:12:05 > 0:12:09and the first time it had ever been attempted on this scale.
0:12:09 > 0:12:11The result is a triumph.
0:12:12 > 0:12:16A bridge that many thought would be impossible to build.
0:12:18 > 0:12:2375 years later, the rail bridge was joined by a second crossing,
0:12:23 > 0:12:25the road bridge.
0:12:25 > 0:12:30The longest suspension bridge in Europe when it was built in 1964.
0:12:32 > 0:12:37And today, these two are being joined by a third -
0:12:37 > 0:12:39the Queensferry Crossing.
0:12:41 > 0:12:46With its three towers each over 200 metres tall, that's twice
0:12:46 > 0:12:50as tall as the railway bridge, it'll be completed in 2016.
0:12:53 > 0:12:56Three bridges, each from a different century.
0:13:01 > 0:13:05But all using the same pioneering techniques of the rail bridge,
0:13:05 > 0:13:06to anchor them to the seabed.
0:13:12 > 0:13:16Not only are these three bridges such powerful icons of British
0:13:16 > 0:13:20engineering, they also represent the importance of keeping
0:13:20 > 0:13:22the country connected and moving.
0:13:25 > 0:13:27They're not just symbols of the country,
0:13:27 > 0:13:30they are symbols of a dynamic nation.
0:13:41 > 0:13:43I'm on my way to somewhere special.
0:13:49 > 0:13:53You might think of it as Britain's first motorway,
0:13:53 > 0:13:56but it's from an era long before cars.
0:13:58 > 0:14:00200 years ago,
0:14:00 > 0:14:05it helped transform a sleepy Britain into a global industrial superpower.
0:14:09 > 0:14:13In those days, coal and iron were needed in huge amounts to feed
0:14:13 > 0:14:18the new industries, so to connect the mines with the factories,
0:14:18 > 0:14:22canals like this were built and they revolutionized Britain.
0:14:23 > 0:14:26Canals got Britain moving like never before.
0:14:30 > 0:14:32But there was a problem.
0:14:32 > 0:14:35The major industrial cities of northern England
0:14:35 > 0:14:39are separated by a high barrier, the Pennine Mountains.
0:14:39 > 0:14:44Going over was impossible. Going around would take far too long.
0:14:45 > 0:14:48And that just left one solution.
0:14:48 > 0:14:50To tunnel straight through.
0:14:50 > 0:14:54But how on earth do you build a tunnel under a mountain?
0:14:57 > 0:14:59Back in the 1790s,
0:14:59 > 0:15:03without the aid of modern machinery, that was no mean feat.
0:15:05 > 0:15:09But here it is, the Standedge Tunnel that passes through the Pennines.
0:15:11 > 0:15:14It was the most ambitious engineering project of its day.
0:15:25 > 0:15:26And after it was finished,
0:15:26 > 0:15:30the only way to get the canal boats through the tunnel was like this.
0:15:34 > 0:15:39So, this is called legging and this is how you propel your boat
0:15:39 > 0:15:42along the canal to the other side, and you would have actually
0:15:42 > 0:15:46had professional leggers doing this, probably a couple on each boat.
0:15:48 > 0:15:53It's a long old push. Three miles and I'm done.
0:15:53 > 0:15:55But it's nothing compared to the task of building
0:15:55 > 0:15:57the tunnel in the first place.
0:16:01 > 0:16:04Back in the day, the canals were called navigations
0:16:04 > 0:16:07and the men that would have built them were called the navigators,
0:16:07 > 0:16:12or navvies for short, and it would have been brutal work.
0:16:16 > 0:16:19In the rough, deeper parts of the tunnel,
0:16:19 > 0:16:23you can see some distinctive marks left behind.
0:16:23 > 0:16:26They're an important clue as to how you build a tunnel through
0:16:26 > 0:16:28a mountain by hand and a few tools.
0:16:30 > 0:16:34This is a star drill. This is the original tool that the
0:16:34 > 0:16:36navvies would have used.
0:16:36 > 0:16:38You can see why it's called a star drill - you've got this cross
0:16:38 > 0:16:43at one end and you would have had a couple of guys, with sledgehammers,
0:16:43 > 0:16:46banging this end and then every bang you would have done a little quarter
0:16:46 > 0:16:50turn, and then banged it again and then a little quarter turn,
0:16:50 > 0:16:52but just imagine how long it would have taken
0:16:52 > 0:16:54to make one of those holes.
0:16:54 > 0:16:58You can see how long they are when you look at the ceiling.
0:16:58 > 0:17:01Must have been just utterly back-breaking work.
0:17:03 > 0:17:07To get a sense of the challenge of cutting through solid rock,
0:17:07 > 0:17:10I'm going to try and build a little bit of tunnel myself.
0:17:12 > 0:17:14And I'm going to cheat a bit.
0:17:19 > 0:17:23This pneumatic drill will quickly make a four-foot long hole.
0:17:28 > 0:17:32Once I've completed it, there's another key step the navvies
0:17:32 > 0:17:34had to carry out.
0:17:34 > 0:17:36For this you need some explosives.
0:17:37 > 0:17:40That is some very coarse, black powder
0:17:40 > 0:17:44and that is black powder in a plastic tube,
0:17:44 > 0:17:49with a bit of fuse at the end, just like in Tom and Jerry.
0:17:52 > 0:17:56There we go, just really temp it down, nice and firm.
0:17:56 > 0:17:57Right. We're good to go.
0:17:59 > 0:18:03The fuse gives me just enough time to clear the blast zone.
0:18:03 > 0:18:04And then...
0:18:07 > 0:18:08EXPLOSION
0:18:14 > 0:18:16A nice big bang.
0:18:16 > 0:18:21But after all that, how much rock have I blown away?
0:18:21 > 0:18:26Right, let's have a look. There's a great smell of sulphur.
0:18:27 > 0:18:30That's the opening to the hole there.
0:18:30 > 0:18:32It's really just this bit here.
0:18:32 > 0:18:35Actually the interesting thing is the shape that it's made is
0:18:35 > 0:18:39exactly the same shape that you see... Or the same mark that you
0:18:39 > 0:18:43see in the canal tunnel, on the ceiling and on the walls.
0:18:43 > 0:18:46But actually, it's really not very much. Think about
0:18:46 > 0:18:49that size in context of the canal tunnel.
0:18:51 > 0:18:54It took 17 long years to complete the tunnel,
0:18:54 > 0:18:58blasting and hacking through over three miles of solid rock.
0:19:01 > 0:19:05God, I tell you what, if you've ever complained about your job,
0:19:05 > 0:19:09just imagine what it would have been like to have been a navvy.
0:19:09 > 0:19:14Today, we think of canals as rather restful places.
0:19:14 > 0:19:18But back then, canals would have transported coal, iron, wood -
0:19:18 > 0:19:21all powering our new industries.
0:19:23 > 0:19:27And they carried another raw material that's less well-known -
0:19:27 > 0:19:28silica.
0:19:29 > 0:19:34During the industrial heyday, silica was crucial for smelting metal.
0:19:34 > 0:19:37It could be turned into special bricks that would withstand
0:19:37 > 0:19:40the raging fires of our furnaces.
0:19:49 > 0:19:53Most silica came from Wales where it was mined from deep underground.
0:19:57 > 0:20:00The Dinas Mine closed in 1964.
0:20:01 > 0:20:06But today, it still draws people down into its depths, because deep
0:20:06 > 0:20:11down there is a truly magical world and one of Britain's hidden wonders.
0:20:16 > 0:20:19This is quite a haunting place.
0:20:19 > 0:20:23Everywhere you look you see evidence of long gone human activity.
0:20:23 > 0:20:26You can almost feel the presence
0:20:26 > 0:20:28of the men who would have worked down here.
0:20:32 > 0:20:35When the miners packed up 50 years ago,
0:20:35 > 0:20:37something else took their place.
0:20:37 > 0:20:39Water.
0:20:39 > 0:20:41Millions of litres of water.
0:20:45 > 0:20:50It attracted the attention of a group of extreme sports enthusiasts.
0:20:50 > 0:20:51Cave divers.
0:20:54 > 0:21:00I'm here to experience what it's like to scuba dive, down a mine.
0:21:00 > 0:21:02Most of us instinctively feel pretty anxious
0:21:02 > 0:21:06if we were trapped in an enclosed space, or underwater.
0:21:06 > 0:21:08Here, I'm about to face both.
0:21:12 > 0:21:15Martyn Farr, an experienced cave diver,
0:21:15 > 0:21:17will guide me through its depths.
0:21:19 > 0:21:21How nervous should I be doing this?
0:21:21 > 0:21:25This is probably one of the most dangerous activities in the world.
0:21:25 > 0:21:30You're in a confined tunnel. This is cold, icy water.
0:21:30 > 0:21:32Yeah, it can be dangerous, OK?
0:21:32 > 0:21:36People die doing this activity, that's for sure.
0:21:36 > 0:21:40Well, I was actually hoping for something a little more encouraging.
0:21:41 > 0:21:43After one last safety check, we're off.
0:21:54 > 0:21:58Surrounded, like a tomb of solid stone,
0:21:58 > 0:22:00I immediately feel vulnerable.
0:22:00 > 0:22:02If something goes wrong, I can't simply swim to the
0:22:02 > 0:22:07surface for air, because there is no surface, just a tunnel roof.
0:22:09 > 0:22:13It's a disturbing reminder of how lethal a mistake could be.
0:22:17 > 0:22:20Ahead of me, Martyn lays a safety cable.
0:22:22 > 0:22:26That way, we should be able to find our way back if we get lost.
0:22:28 > 0:22:31And I quickly see why this is so important.
0:22:31 > 0:22:36I'm too close to the tunnel floor and disturb a layer of silt.
0:22:38 > 0:22:40The water turns murky
0:22:40 > 0:22:43and my visibility reduces to just a few inches.
0:22:44 > 0:22:48I can hardly see a thing and it's difficult not to panic,
0:22:48 > 0:22:50but I push on.
0:22:52 > 0:22:57And soon, with a bit more practice, I begin to find my fins.
0:22:57 > 0:23:02And then I see the perilous world of cave diving with different eyes.
0:23:03 > 0:23:08Beneath the surface, the abandoned mine comes alive with colour.
0:23:12 > 0:23:18The walls are a vivid orange because of the purity of the silica in them.
0:23:18 > 0:23:22Air bubbles race across the mine roof, like drops of mercury.
0:23:34 > 0:23:38These old carts and tram lines would have once pulled the silica out.
0:23:44 > 0:23:48And wooden timbers prevented the roof of the mine from collapsing.
0:23:52 > 0:23:55This is the eerie remains of the bustling world
0:23:55 > 0:23:58that used to exist here for two centuries.
0:24:00 > 0:24:03It is odd to think that this flooded mine,
0:24:03 > 0:24:06frozen in time, could be as beautiful as this.
0:24:15 > 0:24:19And I feel a genuine sense of regret when my air starts to run out
0:24:19 > 0:24:20and it's time to leave.
0:24:29 > 0:24:30Oh, wow.
0:24:35 > 0:24:38It's absolutely amazing when you get into those big caverns,
0:24:38 > 0:24:44because the water is just absolutely crystal clear
0:24:44 > 0:24:47and you can just see for miles, but you can understand why people
0:24:47 > 0:24:50get into trouble because it's really, really seductive.
0:24:50 > 0:24:52You get into these open spaces and you just want to explore
0:24:52 > 0:24:56and you want to sort of look around, and it's really easy
0:24:56 > 0:24:59to come a cropper, because all you have to do is kick up some dust
0:24:59 > 0:25:03and you're completely blind.
0:25:03 > 0:25:05Keep an eye on the line.
0:25:05 > 0:25:07That was amazing there.
0:25:07 > 0:25:11Really amazing. New hobby.
0:25:14 > 0:25:17Who'd have thought that such a magical world could exist
0:25:17 > 0:25:19deep below the Welsh countryside?
0:25:25 > 0:25:27Beneath the landscape of Britain,
0:25:27 > 0:25:31there's another hidden kingdom I'm about to explore.
0:25:31 > 0:25:34But this time, it's not one that we've created.
0:25:35 > 0:25:38There are no maps, no architect's drawings.
0:25:38 > 0:25:41It's a world created by some of the other inhabitants who
0:25:41 > 0:25:45live on the Farne Islands, just off the Northumbrian coast.
0:25:47 > 0:25:50There's something beneath my feet that, if you didn't know,
0:25:50 > 0:25:53I reckon you'd be pretty hard pressed to guess what.
0:25:53 > 0:25:56Now, I'll give you a clue - it's a kind of animal,
0:25:56 > 0:25:59but it's not a mole or a rat or anything like that.
0:25:59 > 0:26:02It is, in fact, a bird.
0:26:04 > 0:26:07David Steel is a warden here on the Farne Islands.
0:26:07 > 0:26:09He's hoping to reveal to me
0:26:09 > 0:26:13who's responsible for engineering this subterranean world.
0:26:13 > 0:26:19- No, nothing in that one. - No.- Oh, got one.- Have you?
0:26:19 > 0:26:23Yeah, I've got one. Yes. I've got one, here we go.
0:26:23 > 0:26:25This should be quite interesting fun.
0:26:25 > 0:26:28Here, sir, is an adult puffin.
0:26:28 > 0:26:33- Hi. Hi. Look at you.- Look at that. Say hello to the world.
0:26:33 > 0:26:36Puffins spend most of their lives at sea.
0:26:36 > 0:26:40But when they return to land, they become burrowers.
0:26:40 > 0:26:44You can see how puffins dig out the holes. They've actually got big
0:26:44 > 0:26:47claws, I don't know if you can see them on the end of the feet there.
0:26:47 > 0:26:48Really sharp claws.
0:26:48 > 0:26:51Extremely sharp claws and they'll actually just dig their burrows
0:26:51 > 0:26:55with those claws and their bills, so, that's it.
0:26:55 > 0:27:00They dig so fanatically for one fluffy reason.
0:27:00 > 0:27:03Now, is there a puffling in there? Do we know? I mean...
0:27:03 > 0:27:06Well, I'm hoping so. I'm just going to put him down,
0:27:06 > 0:27:09- just keep him to one side there. - And is he quite happy there?
0:27:09 > 0:27:10He is. I'm going to pass you...
0:27:10 > 0:27:13If I can get the chick out, I'm going to pass my chick to you.
0:27:13 > 0:27:15This is my first puffling.
0:27:15 > 0:27:19So, this will be the first time this puffling has seen
0:27:19 > 0:27:22the outside world, so I'm just going to put it into your hand.
0:27:22 > 0:27:26There you go, sir. If you can just get a bit of grass out of his hair.
0:27:26 > 0:27:28- That's it. - Oh, look. Hi. Hi, there.
0:27:28 > 0:27:31Can you see? Come and meet your adoring public.
0:27:31 > 0:27:34There we go. Look at that. That is a puffling.
0:27:34 > 0:27:38He'll spend about 40 days down this dark, damp hole
0:27:38 > 0:27:40and then under the cover of darkness,
0:27:40 > 0:27:44without parents' consent, he's going to walk to the sea.
0:27:44 > 0:27:47And he'll spend the next three years on the sea,
0:27:47 > 0:27:51before eventually returning to breed as a breeding adult.
0:27:51 > 0:27:55And life for them can be 30, 35 years.
0:27:55 > 0:27:57Now listen, you, I'm going to put you back with your mum
0:27:57 > 0:28:00- in your burrow underground. So, is this right? I just...- Yeah.
0:28:00 > 0:28:02- ..pop him back in?- Put him down.
0:28:04 > 0:28:09Puffins lay only one egg a year,
0:28:09 > 0:28:12so every puffling is precious.
0:28:18 > 0:28:22That's why they dig their burrows up to two metres long to keep
0:28:22 > 0:28:26their young safe from veracious predators such as the great skua.
0:28:34 > 0:28:39With 80,000 puffins here, this is a city of sea birds,
0:28:39 > 0:28:41all tucked safely beneath the ground.
0:28:43 > 0:28:47On these islands, these cute little birds have constructed
0:28:47 > 0:28:49an astonishing complex.
0:28:51 > 0:28:56A staggering 80km of tunnels and burrows.
0:28:56 > 0:29:00Essentially, this is the most excavated piece of real estate
0:29:00 > 0:29:02anywhere in the UK.
0:29:06 > 0:29:11Elsewhere, we share Britain beneath our feet with other animal species.
0:29:13 > 0:29:16And these don't live on remote islands.
0:29:18 > 0:29:21In fact, some of them are positively suburban.
0:29:25 > 0:29:29The village of Clapham in Bedfordshire.
0:29:29 > 0:29:33The local school is under attack from forces beneath the ground.
0:29:37 > 0:29:41On the surface, it just looks like an ordinary primary school,
0:29:41 > 0:29:45but if you look a little bit closer, you can see evidence everywhere
0:29:45 > 0:29:46of a subterranean assault.
0:29:46 > 0:29:50Now, just behind me is the kids' vegetable garden.
0:29:50 > 0:29:53It's now just condemned and forgotten, pitted with these
0:29:53 > 0:29:59lethal potholes and a shed that's teetering on the edge of collapse.
0:29:59 > 0:30:02But who, or what, is responsible?
0:30:05 > 0:30:09With the aid of a night vision camera, the culprits are revealed.
0:30:15 > 0:30:16Badgers.
0:30:16 > 0:30:21And by the looks of it, quite a number.
0:30:21 > 0:30:25Across the UK there are an astonishing 300,000 badgers.
0:30:27 > 0:30:32But all is not well in badger world.
0:30:32 > 0:30:36Badgers live in a sett, which isn't just a simple burrow,
0:30:36 > 0:30:39but a complex of tunnels and chambers.
0:30:39 > 0:30:43The sett can spread for 200 metres or more
0:30:43 > 0:30:45and can be up to six metres deep.
0:30:48 > 0:30:50Their digging is so extensive,
0:30:50 > 0:30:53it can undermine a building's foundations.
0:30:53 > 0:30:56The badgers here are absolutely thriving
0:30:56 > 0:30:59and their sett is expanding fast, which is putting them
0:30:59 > 0:31:03on a collision course with the school about ten metres behind me.
0:31:03 > 0:31:06And obviously, if the badgers start tunnelling under that,
0:31:06 > 0:31:09then that could cause damage to the school, which is not what you want,
0:31:09 > 0:31:12so there really is only one solution to the problem -
0:31:12 > 0:31:15the badgers are going to have to move house.
0:31:15 > 0:31:18They're victims of their own success.
0:31:21 > 0:31:24Luckily, help is on hand from Tristram Pearce,
0:31:24 > 0:31:29one of the few people in the country with the skills to save the school.
0:31:29 > 0:31:32You are working with wild animals...
0:31:32 > 0:31:34He's an expert in badger relocation.
0:31:39 > 0:31:42First, we need to build an underground complex
0:31:42 > 0:31:46fit for our badger society, an artificial sett.
0:31:48 > 0:31:52- And how many rooms do we need to do? - We're going to build ten to 12.
0:31:52 > 0:31:54Right. That's quite a lot of work.
0:31:54 > 0:31:56It is, so I've got some help coming over,
0:31:56 > 0:31:59so we pop the lid on here and go and get some help.
0:31:59 > 0:32:00Right. Brilliant.
0:32:00 > 0:32:04It's going to take a group of men armed with heavy machinery to
0:32:04 > 0:32:07replicate the abilities of just six badgers.
0:32:07 > 0:32:09If we could have a few chambers as well, guys.
0:32:09 > 0:32:12Shall I start doing that at the end of the pipe, then?
0:32:12 > 0:32:14Yeah. Good work, Dallas, good work.
0:32:15 > 0:32:17Looking at our effort,
0:32:17 > 0:32:21I'm not entirely convinced this is going to work.
0:32:24 > 0:32:27And we still have to persuade the badgers to move.
0:32:27 > 0:32:32This is where the current sett is, adjacent to the school.
0:32:32 > 0:32:35And these are all the paths used by the badgers
0:32:35 > 0:32:37when they're looking for food at night.
0:32:37 > 0:32:39Our brand-new sett is here,
0:32:39 > 0:32:42right next to this well-trodden badger path.
0:32:43 > 0:32:46We need to entice them to the new sett,
0:32:46 > 0:32:50and when they discover it, they'll love it so much, they'll move in.
0:32:50 > 0:32:53At least that's the theory.
0:32:55 > 0:32:58So, with the building almost complete, I've been sent on a rather
0:32:58 > 0:33:04noxious mission to try and attract the badgers to their new home.
0:33:04 > 0:33:08Here we are. Right. This is what I'm looking for.
0:33:09 > 0:33:11Phwoar! That is ripe!
0:33:11 > 0:33:15This is actually badger poo and the idea is we're going to try
0:33:15 > 0:33:19and use this as a scent trail to entice them from here to the
0:33:19 > 0:33:23palatial splendour of the new sett we're building over there.
0:33:27 > 0:33:30And while Tristram's team bury our work beneath a few tonnes of
0:33:30 > 0:33:36fresh earth, I have the unenviable task of laying the poo trail.
0:33:37 > 0:33:40Oh, God! It stinks!
0:33:40 > 0:33:44Literally leading the badgers by the nose to their new home.
0:33:44 > 0:33:48Not the most glamorous job I've ever had.
0:33:48 > 0:33:51OK, I think we're good here. We've built the sett, we've laid
0:33:51 > 0:33:55our poo scent trail, we've got this whole area now as badgery
0:33:55 > 0:34:00as we can get it. I think our work is done, just add badger now.
0:34:04 > 0:34:08It's been three months, and I've come back to Clapham to find out
0:34:08 > 0:34:10have the badgers moved into their des-res?
0:34:13 > 0:34:16It's really started to blend in to the environment,
0:34:16 > 0:34:17it's all covered in grass.
0:34:17 > 0:34:20This was just a big pile of mud when we started.
0:34:20 > 0:34:23We're going to set up a couple of night vision cameras,
0:34:23 > 0:34:25round about here,
0:34:25 > 0:34:31and lay some bait and then see if they've moved in.
0:34:31 > 0:34:35- MIMICKING LLOYD GROSSMAN:- Who lives in a house like this?
0:34:35 > 0:34:38Peanut butter. Stick.
0:34:46 > 0:34:48Peanuts.
0:34:48 > 0:34:52The night vision cameras will help me see in the pitch-black.
0:34:53 > 0:34:55Keep our fingers crossed.
0:34:59 > 0:35:02With everything set, all we have to do now is wait.
0:35:09 > 0:35:11And wait.
0:35:12 > 0:35:18After an hour, still nothing's happened. Are they here at all?
0:35:18 > 0:35:22Shhh, shhh! There, there. Look, look, look. Just there.
0:35:25 > 0:35:29He's coming this way. Look, it's coming over. Oh, my God, look.
0:35:32 > 0:35:35Oh, look at that. Amazing.
0:35:41 > 0:35:44I wasn't sure how this was going to turn out at all when we built
0:35:44 > 0:35:47this three months ago, but, you know, we've seen some badgers
0:35:47 > 0:35:49and they obviously really, really like it.
0:35:49 > 0:35:52They're obviously very happy. It gives them a place to live,
0:35:52 > 0:35:54they're secure, it gives them refuge.
0:35:57 > 0:36:01Means the school isn't going to fall down, so it's a win-win.
0:36:04 > 0:36:07We're learning how to share the Britain beneath our feet with
0:36:07 > 0:36:11animals like these badgers, who build their whole world underground.
0:36:14 > 0:36:17But it's extraordinary to think that there might have been a time
0:36:17 > 0:36:21when every one of us had to look underground to survive.
0:36:25 > 0:36:28I've come to the outskirts of Edinburgh to uncover
0:36:28 > 0:36:32a place that belongs to a secretive and sinister era.
0:36:38 > 0:36:44This is an old BBC studio that was kitted out over 50 years ago.
0:36:44 > 0:36:48And it's interesting because in all that time,
0:36:48 > 0:36:53it's never ever been used as a studio before, until today.
0:36:53 > 0:36:57And it's just as well, because its sole function was to relay
0:36:57 > 0:36:59some pretty devastating information.
0:37:01 > 0:37:05RECORDING: 'This is the wartime broadcasting service.
0:37:05 > 0:37:08'This country has been attacked with nuclear weapons.
0:37:08 > 0:37:11'Communications have been severely disrupted and the number
0:37:11 > 0:37:15'of casualties and the extent of the damage are not yet known.
0:37:15 > 0:37:19'We shall bring you further information as soon as possible.
0:37:19 > 0:37:23'Meanwhile, stay tuned to this wavelength, stay calm,
0:37:23 > 0:37:25'and stay in your own house.'
0:37:30 > 0:37:33Listening to that today,
0:37:33 > 0:37:37it almost feels inconceivable that we got ourselves
0:37:37 > 0:37:39into that situation.
0:37:39 > 0:37:44Can you imagine hearing information like that today, how you'd feel?
0:37:56 > 0:37:59When this place was set up, the government wasn't being paranoid.
0:38:01 > 0:38:05In the 1950 and '60s, Russia and the West were on the brink
0:38:05 > 0:38:07of nuclear war.
0:38:09 > 0:38:12During the Cuban Missile Crisis, we came closer than ever to
0:38:12 > 0:38:14annihilation.
0:38:15 > 0:38:20JFK: 'It shall be the policy of this nation to regard any nuclear missile
0:38:20 > 0:38:23'launched from Cuba against any nation in the western hemisphere
0:38:23 > 0:38:26'as an attack by the Soviet Union on the United States.'
0:38:30 > 0:38:33And in this tense political atmosphere,
0:38:33 > 0:38:35Barnton Bunker came about.
0:38:36 > 0:38:40A top-secret complex to be occupied in the event of an all-out
0:38:40 > 0:38:41nuclear attack.
0:38:46 > 0:38:49Today, a team of dedicated volunteers is attempting
0:38:49 > 0:38:53the slow and arduous task of restoring the bunker.
0:38:56 > 0:38:59Eventually, they plan to turn it into a museum.
0:39:01 > 0:39:04But back in the Cold War, it was designed to withstand
0:39:04 > 0:39:06the destructive blast of a nuclear bomb.
0:39:13 > 0:39:18I've got hold of some amazing old documents connected to the
0:39:18 > 0:39:21site from when it was built and you can see here, all round
0:39:21 > 0:39:25the building, it's surrounded by ten feet of concrete and down
0:39:25 > 0:39:29here you can see where the blast doors would be, which are enormous.
0:39:29 > 0:39:33They weigh over a tonne each and, perhaps even more importantly,
0:39:33 > 0:39:35you've got the ventilation system and this room that we're
0:39:35 > 0:39:39in here are the kind of remains of that ventilation system. Over here
0:39:39 > 0:39:42you've got a giant cooling unit and this bit here is the actual
0:39:42 > 0:39:46filters that would have filtered out some of the radioactive particles.
0:39:54 > 0:40:00The complex is enormous. 50 rooms spread over three floors.
0:40:00 > 0:40:04Its generators and air filtration systems making it entirely
0:40:04 > 0:40:06self-contained.
0:40:06 > 0:40:10It would have held a key group of 420 people,
0:40:10 > 0:40:14considered vital to keep the country running.
0:40:14 > 0:40:17A cross-section of society, buried
0:40:17 > 0:40:21and sealed off from the outside world, 40 feet below the surface.
0:40:24 > 0:40:28Barnton Bunker in Edinburgh, was only one of a network
0:40:28 > 0:40:32of 12 regional command bunkers spread across the UK.
0:40:33 > 0:40:37It was from these that the country would have been run in the
0:40:37 > 0:40:41event of a nuclear war, all linked by a secure telephone network.
0:40:45 > 0:40:47It's startling to think that thousands of people would
0:40:47 > 0:40:51have lived underground, possibly for years.
0:40:51 > 0:40:55Could society really have survived in this way?
0:40:58 > 0:41:01Fortunately, we never had to find out,
0:41:01 > 0:41:04but places like these, like this bunker deep beneath me
0:41:04 > 0:41:08that I'm standing on top of, are a really important part of our
0:41:08 > 0:41:11recent history and they deserve to be restored, so that future
0:41:11 > 0:41:17generations can see just how close we did come to self-annihilation.
0:41:21 > 0:41:24Barnton Bunker is a chilling reminder of a world
0:41:24 > 0:41:26on a permanent war footing.
0:41:27 > 0:41:28But at other times,
0:41:28 > 0:41:31we've gone underground for much more peaceful purposes.
0:41:39 > 0:41:42The mountains of Snowdonia.
0:41:42 > 0:41:45Majestic. Untamed.
0:41:45 > 0:41:47And yet hidden among them
0:41:47 > 0:41:51is a place we all rely on without even realising.
0:41:54 > 0:41:56It's absolutely breathtaking.
0:41:56 > 0:41:58There are few places in Britain where you feel
0:41:58 > 0:42:03this close to nature and it's a wild refuge for many plants
0:42:03 > 0:42:05and animals that would struggle to live elsewhere.
0:42:08 > 0:42:13But for one particular mountain, that wilderness is only skin deep.
0:42:14 > 0:42:17Mount Elidir has a secret beneath its surface.
0:42:24 > 0:42:27To find out what it is, I'm actually driving into the heart
0:42:27 > 0:42:29of the mountain.
0:42:29 > 0:42:33It's like entering the lair of a Bond super villain.
0:42:33 > 0:42:36But below this mountain is something far more useful.
0:42:38 > 0:42:39Dinorwig Power Station.
0:42:43 > 0:42:47These massive turbines make it one of the largest hydroelectric
0:42:47 > 0:42:51power stations of its kind in the world, specifically built to
0:42:51 > 0:42:53provide a rapid response in a crisis.
0:42:59 > 0:43:03100 metres underground, Dean Mannion has an impressive
0:43:03 > 0:43:06amount of power at his fingertips.
0:43:06 > 0:43:09In terms of the number of homes, how many homes could you power?
0:43:09 > 0:43:13Well, we should be able to provide enough energy for most of say
0:43:13 > 0:43:16something like Manchester for about six hours now,
0:43:16 > 0:43:18up to nearly six hours.
0:43:18 > 0:43:19ALARM BEEPING
0:43:19 > 0:43:22Suddenly, we're interrupted by an alarm.
0:43:22 > 0:43:26- What did you look at on the screen? - Here? That's flashing red now.
0:43:26 > 0:43:29- So SG means...- Spin-gen. - Spin generator.
0:43:29 > 0:43:32And that's on Ffestiniog three.
0:43:32 > 0:43:36Dinorwig exists to make lots of electricity, fast.
0:43:36 > 0:43:39And Dean has just received an urgent demand for more power.
0:43:41 > 0:43:45These emergencies happen all the time, like at the end of a huge
0:43:45 > 0:43:49sporting event on the telly, when everyone pops the kettle on.
0:43:51 > 0:43:54That leads to a huge spike in demand for electricity.
0:43:56 > 0:43:58The power there's just coming up.
0:43:58 > 0:44:00So, 18 megawatts, 24 megawatts.
0:44:02 > 0:44:03With the flick of a switch,
0:44:03 > 0:44:08Dean's created enough power from the water to provide for a whole city.
0:44:08 > 0:44:12There we are, we're up to 92 megawatts. There we go.
0:44:12 > 0:44:14So, in a way, it is magic.
0:44:14 > 0:44:17If you can imagine, we've done that with nothing but water.
0:44:17 > 0:44:22Dinorwig's secret is a lake high up in the mountain.
0:44:22 > 0:44:27As soon as the alarm goes off, Dean releases the water held in the lake.
0:44:27 > 0:44:31It tears down the network of pipes, cascading through the mountain,
0:44:31 > 0:44:33until it enters here.
0:44:35 > 0:44:36The turbine hall.
0:44:37 > 0:44:41The torrent is funnelled through six huge generating units.
0:44:43 > 0:44:47This creates more than enough power to meet the vast demand
0:44:47 > 0:44:49in just 12 seconds.
0:44:49 > 0:44:53That's 30 times quicker than any normal power station.
0:44:55 > 0:44:58Electricity then floods into the national grid
0:44:58 > 0:44:59along underground cables.
0:45:06 > 0:45:10We're about 600 meters below the lake up at the top.
0:45:10 > 0:45:14So, when the water gets down to this level, it's under huge
0:45:14 > 0:45:18amounts of pressure. It comes in this vast, vast pipe here,
0:45:18 > 0:45:21and this is the valve, so it can either be open or closed.
0:45:21 > 0:45:23At the moment it's closed, and these yellow things here,
0:45:23 > 0:45:28these huge counterweights, are what open and close the valve.
0:45:28 > 0:45:32But as much water passes through that valve in
0:45:32 > 0:45:3790 minutes as is used by London in an entire day.
0:45:39 > 0:45:44All that water powering through turbines comes with a risk attached.
0:45:46 > 0:45:49This is Shushenskaya Power Station in Russia.
0:45:52 > 0:45:56One day in August, 2009, workers noticed the entire building
0:45:56 > 0:45:58starting to vibrate.
0:45:59 > 0:46:01And then this happened.
0:46:05 > 0:46:09A 1,500 tonne turbine was flung
0:46:09 > 0:46:1315 metres into the air, propelled by a huge column of water.
0:46:16 > 0:46:23It blasted through the building and 75 people died.
0:46:26 > 0:46:31So at Dinorwig, harnessing the power of all that water safely
0:46:31 > 0:46:33is an extraordinary feat of engineering.
0:46:43 > 0:46:47But the water of the lake doesn't last forever.
0:46:47 > 0:46:48This is the end of the process.
0:46:48 > 0:46:51So, you've generated your electricity, the water's come
0:46:51 > 0:46:55all the way down there and ended up here at the bottom of the mountain.
0:46:56 > 0:47:01And for most hydro-electric power stations, that would be that.
0:47:01 > 0:47:03But Dinorwig has one last trick.
0:47:05 > 0:47:08At night, spare electricity is used to throw the whole
0:47:08 > 0:47:10process into reverse.
0:47:12 > 0:47:15The machinery pumps water back up to the lake at the
0:47:15 > 0:47:19top of the mountain, where it sits ready to be released again.
0:47:21 > 0:47:24Dinorwig is like a mountain-sized rechargeable battery
0:47:24 > 0:47:26that can be used over and over.
0:47:28 > 0:47:32It's power available instantly at the flick of a switch.
0:47:38 > 0:47:42The power station that's buried deep inside electric mountain harnesses
0:47:42 > 0:47:46water to solve that tricky problem of being able to store and then
0:47:46 > 0:47:51release very quickly huge amounts of energy, and it is an amazing thought
0:47:51 > 0:47:55when you think of things as mundane as making a cup of tea or charging
0:47:55 > 0:48:01your mobile phone or watching TV, you're actually plugging into that.
0:48:04 > 0:48:06Over the last two centuries,
0:48:06 > 0:48:10we've created a whole world of connections underground.
0:48:10 > 0:48:15Pipelines, water mains, power and superhighways.
0:48:15 > 0:48:17All essential to keep the country running.
0:48:22 > 0:48:24And in our busiest city,
0:48:24 > 0:48:29we've long relied on the world below our feet to keep people on the move.
0:48:31 > 0:48:35London's Tube network has over 110 miles of tunnels.
0:48:39 > 0:48:41During rush hour alone,
0:48:41 > 0:48:45two million people go to work on the underground.
0:48:45 > 0:48:50Now, that is enough to repopulate Birmingham twice over.
0:48:50 > 0:48:53But every year, the underground is getting even more
0:48:53 > 0:48:56crammed as more and more people head for the capital.
0:48:58 > 0:49:01To ease the inevitable congestion,
0:49:01 > 0:49:04a new network is being built under the streets of London.
0:49:04 > 0:49:09It's called Crossrail and, unlike the Tube, it's a full-sized railway.
0:49:09 > 0:49:12But there is a problem, because the engineers,
0:49:12 > 0:49:16when building this, aren't starting with a blank canvas.
0:49:16 > 0:49:20Beneath the surface, London is a very, very busy place.
0:49:23 > 0:49:27The first underground railway arrived in 1863.
0:49:27 > 0:49:31It linked Paddington in the west, to Farringdon in the east.
0:49:34 > 0:49:37More lines followed in quick succession to keep
0:49:37 > 0:49:40the population of the booming city moving.
0:49:40 > 0:49:44And today, this is what the real Tube map of London looks like.
0:49:46 > 0:49:50But beneath the surface, it's even more complex.
0:49:57 > 0:49:59Foundations.
0:50:01 > 0:50:03Underground stations.
0:50:05 > 0:50:09And a web of tunnels all jostle for space.
0:50:11 > 0:50:15This is about to be joined by the tunnels of Crossrail.
0:50:17 > 0:50:21The biggest construction project in Europe, with a price tag to match.
0:50:21 > 0:50:24£15 billion.
0:50:26 > 0:50:29But how can you build something so massive
0:50:29 > 0:50:31without hitting anything else down here?
0:50:34 > 0:50:37I'm travelling along a section of the new Crossrail tunnel,
0:50:37 > 0:50:40somewhere beneath the streets of east London.
0:50:42 > 0:50:46Ahead of me is the technology that makes the whole project possible.
0:50:52 > 0:50:55This appears to be a construction site,
0:50:55 > 0:50:59but I've actually climbed inside the bowels of one gigantic machine.
0:51:03 > 0:51:04This is a tunnel boring machine,
0:51:04 > 0:51:07or TBM as it's known around these parts.
0:51:07 > 0:51:11It doesn't really look like a machine at all. It resembles
0:51:11 > 0:51:15much more a factory or a production line, lots of different parts
0:51:15 > 0:51:19doing lots of different jobs. It's absolutely enormous.
0:51:19 > 0:51:22They've given it a name, they've called it Ellie.
0:51:22 > 0:51:26Ellie is so big, she has to be assembled beneath the surface.
0:51:28 > 0:51:31She's one of eight tunnelling machines.
0:51:31 > 0:51:34Completed, each is over 100 metres long
0:51:34 > 0:51:36and weighs over 1,000 tonnes.
0:51:38 > 0:51:43She tears her way through London with this, a huge cutting disc.
0:51:43 > 0:51:45It chews through the earth
0:51:45 > 0:51:49with enough force to lift 600 London buses.
0:51:49 > 0:51:52Just imagine the damage this could do if you took a wrong turn.
0:51:56 > 0:52:00And yet the controls are extremely delicate.
0:52:00 > 0:52:03Reginald Swift is Ellie's driver.
0:52:03 > 0:52:07He uses a guidance system to keep the machine on track.
0:52:07 > 0:52:09There's a GPS system at the back of the machine,
0:52:09 > 0:52:12which records where we've been, where we're heading to.
0:52:12 > 0:52:15At the moment, we are two millimetres offline.
0:52:15 > 0:52:18Two millimetres offline, I can't believe it!
0:52:18 > 0:52:21- Is that OK, two millimetres? - That's pretty good, yeah.
0:52:21 > 0:52:23And how fast are we going?
0:52:23 > 0:52:26Speed wise, depending on the ground conditions, anything from,
0:52:26 > 0:52:2930 millimetres a minute to 100 millimetres a minute,
0:52:29 > 0:52:30depending on the ground conditions.
0:52:30 > 0:52:32So, 100 millimetres, that's your top speed?
0:52:32 > 0:52:35- That's your land speed record? - That's the top speed.- OK.
0:52:35 > 0:52:38But what amazes me is the fact that, you know, you have to drill
0:52:38 > 0:52:42under London where there's lots of structures, lots of tunnels,
0:52:42 > 0:52:47lots of things already there, so how close can you go to these safely?
0:52:47 > 0:52:49We've been within 300 millimetres,
0:52:49 > 0:52:54one foot off, I think, the Northern Line at one time.
0:52:54 > 0:52:57- A foot off the Northern Line? - Yeah, one of them anyway.
0:52:57 > 0:53:00That's incredibly close.
0:53:00 > 0:53:01It's amazing that something
0:53:01 > 0:53:06so big can tunnel through the ground without damaging anything around it.
0:53:07 > 0:53:10And as Ellie heaves her way through the ground,
0:53:10 > 0:53:14she leaves the completed tunnel behind her.
0:53:14 > 0:53:17They're just getting ready to install some of these huge concrete
0:53:17 > 0:53:21panels that you can see, which line the tunnel to give it strength.
0:53:31 > 0:53:34It's an amazing process. They've got this huge robot,
0:53:34 > 0:53:38that sucks the panels up and then sticks them onto the wall.
0:53:38 > 0:53:44The accuracy of all of this is stunning. Millimetre precision.
0:53:44 > 0:53:49So, they've completed a whole ring now, which lines the tunnel.
0:53:49 > 0:53:52Without these rings, the whole tunnel could collapse
0:53:52 > 0:53:55in on itself, almost as quickly as it was built.
0:53:56 > 0:54:00Bad for the tunnel and catastrophic for anything that sits above.
0:54:02 > 0:54:06In Egypt, a TBM like Ellie was tunnelling beneath the streets of
0:54:06 > 0:54:11Cairo when just one single concrete panel of the tunnel lining gave way.
0:54:11 > 0:54:16The result? A 20-metre hole in the middle of the road.
0:54:22 > 0:54:25But Crossrail's engineers face even greater challenges than just
0:54:25 > 0:54:27building tunnels.
0:54:27 > 0:54:30Crossrail also requires stations.
0:54:30 > 0:54:35Huge underground labyrinths with concourses, platforms,
0:54:35 > 0:54:39connecting tunnels, escalators and ventilation shafts.
0:54:41 > 0:54:44Building all this means breaking out of the safety of the tunnel's
0:54:44 > 0:54:49concrete ring and digging out into unsupported mud and clay.
0:54:50 > 0:54:52A particularly risky operation.
0:54:57 > 0:55:01To see how difficult building a new station really is,
0:55:01 > 0:55:04I've come to the Crossrail site at Farringdon.
0:55:04 > 0:55:09When completed, 140 trains per hour will pass through here,
0:55:09 > 0:55:12making it one of the busiest stations in the country.
0:55:12 > 0:55:15It calls for a huge amount of work, which is going on
0:55:15 > 0:55:17at the bottom of this hole.
0:55:21 > 0:55:24Nisrine Chartouny is the engineer in charge.
0:55:25 > 0:55:29Key to her work is the concrete rings I saw being inserted earlier.
0:55:31 > 0:55:33- These rings are sacrificial rings. - Sacrificial rings?
0:55:33 > 0:55:36Sacrificial, so they serve a purpose in life, they're only here
0:55:36 > 0:55:40temporarily, and then we take them out and we actually enlarge
0:55:40 > 0:55:44the area around these rings to make a platform tunnel which is
0:55:44 > 0:55:4911 metre in diameter, versus the six metre that we have now.
0:55:49 > 0:55:52Removing the protective rings means there's now nothing
0:55:52 > 0:55:55supporting the tonnes of mud and clay above.
0:55:57 > 0:56:01The crumbling clay needs to be sprayed with concrete.
0:56:01 > 0:56:04It's precise work that has to be done quickly.
0:56:04 > 0:56:08We follow this spray concrete lining method, so you do it in three
0:56:08 > 0:56:11phases, and it's always staggered, so you start with the top,
0:56:11 > 0:56:13the middle and the bottom section
0:56:13 > 0:56:15and this way you control ground movement.
0:56:15 > 0:56:18It's all about controlling ground movement on the surface.
0:56:18 > 0:56:21Without this ingenious technique, the busy streets of Farringdon
0:56:21 > 0:56:23would start to sink.
0:56:24 > 0:56:27The concrete sets hard into a solid layer
0:56:27 > 0:56:31and acts just like the rings of the TBM.
0:56:31 > 0:56:35And that keeps everything above ground exactly where it should be.
0:56:37 > 0:56:40Back on the surface, it is almost hard to believe that
0:56:40 > 0:56:44a project of that scale is going on below me, right where I'm standing.
0:56:44 > 0:56:49It is almost as if they're doing it in secret, when nobody's looking.
0:56:49 > 0:56:54It's that combination of brute force, of precision and elegance
0:56:54 > 0:56:58that makes this a testament to the ingenuity of modern engineering.
0:57:01 > 0:57:07When Crossrail opens in 2016 and an estimated 200 million Londoners
0:57:07 > 0:57:11start to use it every year, we'll be more reliant than ever
0:57:11 > 0:57:14on what goes on hidden beneath the streets.
0:57:19 > 0:57:22Travelling around Britain making this programme, you start
0:57:22 > 0:57:28to understand our familiar landscape in a completely different way.
0:57:28 > 0:57:31So much of what we take for granted in our modern world would be
0:57:31 > 0:57:34inconceivable without what happens below the earth.
0:57:36 > 0:57:39I've discovered how the tallest building in Britain can
0:57:39 > 0:57:41stand on the softest ground.
0:57:47 > 0:57:49How every time we fly on holiday,
0:57:49 > 0:57:53we rely on an underground pipeline that helped us win the war.
0:57:56 > 0:57:59And I found some of the country's most spectacular landscapes
0:57:59 > 0:58:01hidden underground.
0:58:05 > 0:58:08A remarkable range of vibrant connections
0:58:08 > 0:58:12and networks hidden below the familiar world we know so well.
0:58:13 > 0:58:15Quite simply,
0:58:15 > 0:58:19Britain would be impossible without the wonders beneath our feet.