On the Move Britain Beneath Your Feet

This is the Britain we know.

A patchwork of fields, forests, of rugged mountains,

and dramatic skylines.

But ours is also a land of secrets that you can only see

if you look at it in a new way.

From beneath.

I'm going to show you Britain as you've never seen it before.

A hidden, vibrant world that we rely on every day to keep

the country moving.

Bustling with life, unseen beneath our feet.

I'm going to explore the secret superhighways we've created

over 200 years.

Whichever way you look at it, this is a marvel of engineering,

even by modern standards.

I'll see how London's newest railway

is forging its way beneath the streets.

The accuracy of all of this is stunning as well,

it's millimetre precision.

And how some of the most magical parts of our country

are deep below the ground.

That was amazing. Really amazing.

I'm going to discover how everything that we see in our thriving, vibrant

Britain can only really function because of what we can't see.

A secret world of networks, of connections that are hidden

underground.

I'm starting at Heathrow. The busiest airport in Europe.

But this is an airport with a secret.

One you wouldn't guess from the familiar hectic

world of the terminal.

There's another world,

invisible to the eye, that's key to getting you into the air.

72 million people came through here last year,

which works out at nearly half a million flights.

Every one of those flights needs fuel.

We burn through nearly 14 billion litres of aviation fuel a year.

If all that fuel were carried on the roads, then the petrol tankers

would clog up the entire British motorway network,

which makes you think, where is all that extra traffic?

The answer lies in a secret world underground,

that came into existence during Britain's darkest days.

AIR RAID SIREN

It all began in World War II with the Battle of Britain.

The nation's survival depended on the RAF defeating

the German Luftwaffe.

So, it was crucial to keep our planes in the air.

Now, if an army marches on its stomach,

then a plane flies on its fuel tank.

And a new breed of fighter aircraft that were designed to protect

Britain in the Second World War, like the Spitfire or the Hurricane,

were incredibly thirsty beasts. In fact, the future of the nation

really did depend on being able to get enough fuel to these planes.

Fuel was too precious to keep above ground,

where a well aimed bomb could blow it up.

So, the RAF began to do something clever to keep fuel

out of harm's way.

I think this might be fun.

Up we go.

As we fly over the Wiltshire countryside, I'm going

to try to spot it from this original World War II reconnaissance plane.

Oh, what a great view.

They made sure it was well hidden.

In fact, so well hidden, it's hard to find.

OK, so, there it is, you can just see it, the Micheldever Fuel Depot.

It doesn't really look like much at all, you can

just see these two ridges.

There's actually a whole load of fuel tanks buried underneath there,

concealing the important aviation fuel.

As more fuel was needed, more underground fuel stores

like Micheldever were being built,

but there was another problem, because there were only two

sea ports that could distribute the fuel to the various stores -

Avonmouth in the south and Merseyside in the north.

From there, all fuel had to be transported by lorry,

making it vulnerable to attack.

So, in 1941, the RAF hatched an even more

ambitious plan,

which was to send all that fuel underground.

It began simply enough, with an underground pipeline joining

Merseyside to Avonmouth.

North and south were now connected, but fuel was needed

in airfields in the east,

so working secretly at night, engineers extended

the underground fuel network to Kent, East Anglia and Lincolnshire.

The pipeline now criss-crossed the country,

delivering fuel without ever going near the surface.

This was the GPSS, or Government Pipeline and Storage System.

We're actually flying right along one of the pipelines now, but of

course you'd never know flying above here. Completely buried, there's

absolutely no evidence at all, which is exactly what the British wanted.

The pipeline remained secret throughout the war.

It kept our air force flying

and helped turn the tide in the allies' favour.

And remarkably, we still need this same pipeline to get us

into the air today.

This is how Heathrow Terminal Five looks from below.

Once an RAF base, it's now one of the busiest

airports in the world. 1,200 aircraft use it every day.

All this is only possible

thanks to the intricate system of fuel pipes hidden underground.

Each pipe delivers fuel from right across the country,

direct to a plane at its stand.

Beyond Heathrow, Manchester, Gatwick and Stansted are all also connected.

In fact, half of all the aviation fuel used passes through

a direct descendent of the old wartime pipelines.

It's extraordinary to think that the underground network that gets us

on holiday today is the same one which helped us win the war.

As a nation, we're always on the move.

We make more journeys than ever before.

This pushes engineering to the limit.

And there's a place in Britain where, over the last two centuries,

this has played out in a spectacular way.

These are the huge bridges that span the Firth of Forth, connecting

the Highlands of Scotland to the rest of the country.

But the secret that makes all this possible is deep beneath the seabed.

Before it was built, the only way to cross the Firth of Forth was

to head up to Stirling, which is that way, which is going to add

another 60-odd miles to your journey, or do what I'm doing.

Neither of which are ideal. Not what you'd expect

from a connected country.

So, in the 1880s,

Victorian engineers decided to build a bridge.

It is such a familiar landmark, it's almost impossible to

imagine just how radical it was when it was built,

but the world had seen nothing like it.

The Forth Rail Bridge was the biggest bridge in the world

and the first made entirely from steel.

55,000 tonnes of it.

More than 4,500 men worked on it for eight years.

I'll tell you what, actually being this close,

you get a view of the bridge that you never normally get

and suddenly it becomes a completely different structure almost.

You can actually get really, really close and see the rivets themselves.

You can actually see how the whole thing is put together.

Obviously it takes some pretty spectacular engineering to build

something like this, particularly at the time it was built, but

just for a moment, ignore all that majestic metal work above us

and just concentrate on these piles, because the real genius

of this bridge is what's going on here, actually beneath the water.

So, to really appreciate what made the bridge such an engineering

triumph, we need to view it from deep below the waves.

Seen from this perspective,

the foundations take on a whole new prominence.

Great stones piles stretch nearly 30 metres below the water,

anchoring the bridge to the seabed.

Building them was a massive engineering challenge.

Foundations for a structure this size would be

tricky enough on land.

Underwater takes the problem to a whole new level.

What they did was lower huge metal cylinders or caissons to the seabed.

I've got a copy of the original plans made of the caissons

and they're fascinating.

They really capture how they work.

So, once the caisson is actually put in place and weighed down,

what you then have to do is pump all that water out using compressed air.

And this is the clever bit here. You create this

gap at the bottom, about 70 feet below the surface, and the men

would actually work here in the most horrifically dangerous conditions,

actually building the foundation and anchoring the bridge to the seabed.

It's a brilliant solution

and the first time it had ever been attempted on this scale.

The result is a triumph.

A bridge that many thought would be impossible to build.

75 years later, the rail bridge was joined by a second crossing,

the road bridge.

The longest suspension bridge in Europe when it was built in 1964.

And today, these two are being joined by a third -

the Queensferry Crossing.

With its three towers each over 200 metres tall, that's twice

as tall as the railway bridge, it'll be completed in 2016.

Three bridges, each from a different century.

But all using the same pioneering techniques of the rail bridge,

to anchor them to the seabed.

Not only are these three bridges such powerful icons of British

engineering, they also represent the importance of keeping

the country connected and moving.

They're not just symbols of the country,

they are symbols of a dynamic nation.

I'm on my way to somewhere special.

You might think of it as Britain's first motorway,

but it's from an era long before cars.

200 years ago,

it helped transform a sleepy Britain into a global industrial superpower.

In those days, coal and iron were needed in huge amounts to feed

the new industries, so to connect the mines with the factories,

canals like this were built and they revolutionized Britain.

Canals got Britain moving like never before.

But there was a problem.

The major industrial cities of northern England

are separated by a high barrier, the Pennine Mountains.

Going over was impossible. Going around would take far too long.

And that just left one solution.

To tunnel straight through.

But how on earth do you build a tunnel under a mountain?

Back in the 1790s,

without the aid of modern machinery, that was no mean feat.

But here it is, the Standedge Tunnel that passes through the Pennines.

It was the most ambitious engineering project of its day.

And after it was finished,

the only way to get the canal boats through the tunnel was like this.

So, this is called legging and this is how you propel your boat

along the canal to the other side, and you would have actually

had professional leggers doing this, probably a couple on each boat.

It's a long old push. Three miles and I'm done.

But it's nothing compared to the task of building

the tunnel in the first place.

Back in the day, the canals were called navigations

and the men that would have built them were called the navigators,

or navvies for short, and it would have been brutal work.

In the rough, deeper parts of the tunnel,

you can see some distinctive marks left behind.

They're an important clue as to how you build a tunnel through

a mountain by hand and a few tools.

This is a star drill. This is the original tool that the

navvies would have used.

You can see why it's called a star drill - you've got this cross

at one end and you would have had a couple of guys, with sledgehammers,

banging this end and then every bang you would have done a little quarter

turn, and then banged it again and then a little quarter turn,

but just imagine how long it would have taken

to make one of those holes.

You can see how long they are when you look at the ceiling.

Must have been just utterly back-breaking work.

To get a sense of the challenge of cutting through solid rock,

I'm going to try and build a little bit of tunnel myself.

And I'm going to cheat a bit.

This pneumatic drill will quickly make a four-foot long hole.

Once I've completed it, there's another key step the navvies

had to carry out.

For this you need some explosives.

That is some very coarse, black powder

and that is black powder in a plastic tube,

with a bit of fuse at the end, just like in Tom and Jerry.

There we go, just really temp it down, nice and firm.

Right. We're good to go.

The fuse gives me just enough time to clear the blast zone.

And then...

EXPLOSION

A nice big bang.

But after all that, how much rock have I blown away?

Right, let's have a look. There's a great smell of sulphur.

That's the opening to the hole there.

It's really just this bit here.

Actually the interesting thing is the shape that it's made is

exactly the same shape that you see... Or the same mark that you

see in the canal tunnel, on the ceiling and on the walls.

But actually, it's really not very much. Think about

that size in context of the canal tunnel.

It took 17 long years to complete the tunnel,

blasting and hacking through over three miles of solid rock.

God, I tell you what, if you've ever complained about your job,

just imagine what it would have been like to have been a navvy.

Today, we think of canals as rather restful places.

But back then, canals would have transported coal, iron, wood -

all powering our new industries.

And they carried another raw material that's less well-known -

silica.

During the industrial heyday, silica was crucial for smelting metal.

It could be turned into special bricks that would withstand

the raging fires of our furnaces.

Most silica came from Wales where it was mined from deep underground.

The Dinas Mine closed in 1964.

But today, it still draws people down into its depths, because deep

down there is a truly magical world and one of Britain's hidden wonders.

This is quite a haunting place.

Everywhere you look you see evidence of long gone human activity.

You can almost feel the presence

of the men who would have worked down here.

When the miners packed up 50 years ago,

something else took their place.

Water.

Millions of litres of water.

It attracted the attention of a group of extreme sports enthusiasts.

Cave divers.

I'm here to experience what it's like to scuba dive, down a mine.

Most of us instinctively feel pretty anxious

if we were trapped in an enclosed space, or underwater.

Here, I'm about to face both.

Martyn Farr, an experienced cave diver,

will guide me through its depths.

How nervous should I be doing this?

This is probably one of the most dangerous activities in the world.

You're in a confined tunnel. This is cold, icy water.

Yeah, it can be dangerous, OK?

People die doing this activity, that's for sure.

Well, I was actually hoping for something a little more encouraging.

After one last safety check, we're off.

Surrounded, like a tomb of solid stone,

I immediately feel vulnerable.

If something goes wrong, I can't simply swim to the

surface for air, because there is no surface, just a tunnel roof.

It's a disturbing reminder of how lethal a mistake could be.

Ahead of me, Martyn lays a safety cable.

That way, we should be able to find our way back if we get lost.

And I quickly see why this is so important.

I'm too close to the tunnel floor and disturb a layer of silt.

The water turns murky

and my visibility reduces to just a few inches.

I can hardly see a thing and it's difficult not to panic,

but I push on.

And soon, with a bit more practice, I begin to find my fins.

And then I see the perilous world of cave diving with different eyes.

Beneath the surface, the abandoned mine comes alive with colour.

The walls are a vivid orange because of the purity of the silica in them.

Air bubbles race across the mine roof, like drops of mercury.

These old carts and tram lines would have once pulled the silica out.

And wooden timbers prevented the roof of the mine from collapsing.

This is the eerie remains of the bustling world

that used to exist here for two centuries.

It is odd to think that this flooded mine,

frozen in time, could be as beautiful as this.

And I feel a genuine sense of regret when my air starts to run out

and it's time to leave.

Oh, wow.

It's absolutely amazing when you get into those big caverns,

because the water is just absolutely crystal clear

and you can just see for miles, but you can understand why people

get into trouble because it's really, really seductive.

You get into these open spaces and you just want to explore

and you want to sort of look around, and it's really easy

to come a cropper, because all you have to do is kick up some dust

and you're completely blind.

Keep an eye on the line.

That was amazing there.

Really amazing. New hobby.

Who'd have thought that such a magical world could exist

deep below the Welsh countryside?

Beneath the landscape of Britain,

there's another hidden kingdom I'm about to explore.

But this time, it's not one that we've created.

There are no maps, no architect's drawings.

It's a world created by some of the other inhabitants who

live on the Farne Islands, just off the Northumbrian coast.

There's something beneath my feet that, if you didn't know,

I reckon you'd be pretty hard pressed to guess what.

Now, I'll give you a clue - it's a kind of animal,

but it's not a mole or a rat or anything like that.

It is, in fact, a bird.

David Steel is a warden here on the Farne Islands.

He's hoping to reveal to me

who's responsible for engineering this subterranean world.

-No, nothing in that one.

-No.

-Oh, got one.

-Have you?

Yeah, I've got one. Yes. I've got one, here we go.

This should be quite interesting fun.

Here, sir, is an adult puffin.

-Hi. Hi. Look at you.

-Look at that. Say hello to the world.

Puffins spend most of their lives at sea.

But when they return to land, they become burrowers.

You can see how puffins dig out the holes. They've actually got big

claws, I don't know if you can see them on the end of the feet there.

Really sharp claws.

Extremely sharp claws and they'll actually just dig their burrows

with those claws and their bills, so, that's it.

They dig so fanatically for one fluffy reason.

Now, is there a puffling in there? Do we know? I mean...

Well, I'm hoping so. I'm just going to put him down,

-just keep him to one side there.

-And is he quite happy there?

He is. I'm going to pass you...

If I can get the chick out, I'm going to pass my chick to you.

This is my first puffling.

So, this will be the first time this puffling has seen

the outside world, so I'm just going to put it into your hand.

There you go, sir. If you can just get a bit of grass out of his hair.

-That's it.

-Oh, look. Hi. Hi, there.

Can you see? Come and meet your adoring public.

There we go. Look at that. That is a puffling.

He'll spend about 40 days down this dark, damp hole

and then under the cover of darkness,

without parents' consent, he's going to walk to the sea.

And he'll spend the next three years on the sea,

before eventually returning to breed as a breeding adult.

And life for them can be 30, 35 years.

Now listen, you, I'm going to put you back with your mum

-in your burrow underground. So, is this right? I just...

-Yeah.

-..pop him back in?

-Put him down.

Puffins lay only one egg a year,

so every puffling is precious.

That's why they dig their burrows up to two metres long to keep

their young safe from veracious predators such as the great skua.

With 80,000 puffins here, this is a city of sea birds,

all tucked safely beneath the ground.

On these islands, these cute little birds have constructed

an astonishing complex.

A staggering 80km of tunnels and burrows.

Essentially, this is the most excavated piece of real estate

anywhere in the UK.

Elsewhere, we share Britain beneath our feet with other animal species.

And these don't live on remote islands.

In fact, some of them are positively suburban.

The village of Clapham in Bedfordshire.

The local school is under attack from forces beneath the ground.

On the surface, it just looks like an ordinary primary school,

but if you look a little bit closer, you can see evidence everywhere

of a subterranean assault.

Now, just behind me is the kids' vegetable garden.

It's now just condemned and forgotten, pitted with these

lethal potholes and a shed that's teetering on the edge of collapse.

But who, or what, is responsible?

With the aid of a night vision camera, the culprits are revealed.

Badgers.

And by the looks of it, quite a number.

Across the UK there are an astonishing 300,000 badgers.

But all is not well in badger world.

Badgers live in a sett, which isn't just a simple burrow,

but a complex of tunnels and chambers.

The sett can spread for 200 metres or more

and can be up to six metres deep.

Their digging is so extensive,

it can undermine a building's foundations.

The badgers here are absolutely thriving

and their sett is expanding fast, which is putting them

on a collision course with the school about ten metres behind me.

And obviously, if the badgers start tunnelling under that,

then that could cause damage to the school, which is not what you want,

so there really is only one solution to the problem -

the badgers are going to have to move house.

They're victims of their own success.

Luckily, help is on hand from Tristram Pearce,

one of the few people in the country with the skills to save the school.

You are working with wild animals...

He's an expert in badger relocation.

First, we need to build an underground complex

fit for our badger society, an artificial sett.

-And how many rooms do we need to do?

-We're going to build ten to 12.

Right. That's quite a lot of work.

It is, so I've got some help coming over,

so we pop the lid on here and go and get some help.

Right. Brilliant.

It's going to take a group of men armed with heavy machinery to

replicate the abilities of just six badgers.

If we could have a few chambers as well, guys.

Shall I start doing that at the end of the pipe, then?

Yeah. Good work, Dallas, good work.

Looking at our effort,

I'm not entirely convinced this is going to work.

And we still have to persuade the badgers to move.

This is where the current sett is, adjacent to the school.

And these are all the paths used by the badgers

when they're looking for food at night.

Our brand-new sett is here,

right next to this well-trodden badger path.

We need to entice them to the new sett,

and when they discover it, they'll love it so much, they'll move in.

At least that's the theory.

So, with the building almost complete, I've been sent on a rather

noxious mission to try and attract the badgers to their new home.

Here we are. Right. This is what I'm looking for.

Phwoar! That is ripe!

This is actually badger poo and the idea is we're going to try

and use this as a scent trail to entice them from here to the

palatial splendour of the new sett we're building over there.

And while Tristram's team bury our work beneath a few tonnes of

fresh earth, I have the unenviable task of laying the poo trail.

Oh, God! It stinks!

Literally leading the badgers by the nose to their new home.

Not the most glamorous job I've ever had.

OK, I think we're good here. We've built the sett, we've laid

our poo scent trail, we've got this whole area now as badgery

as we can get it. I think our work is done, just add badger now.

It's been three months, and I've come back to Clapham to find out

have the badgers moved into their des-res?

It's really started to blend in to the environment,

it's all covered in grass.

This was just a big pile of mud when we started.

We're going to set up a couple of night vision cameras,

round about here,

and lay some bait and then see if they've moved in.

-MIMICKING LLOYD GROSSMAN:

-Who lives in a house like this?

Peanut butter. Stick.

Peanuts.

The night vision cameras will help me see in the pitch-black.

Keep our fingers crossed.

With everything set, all we have to do now is wait.

And wait.

After an hour, still nothing's happened. Are they here at all?

Shhh, shhh! There, there. Look, look, look. Just there.

He's coming this way. Look, it's coming over. Oh, my God, look.

Oh, look at that. Amazing.

I wasn't sure how this was going to turn out at all when we built

this three months ago, but, you know, we've seen some badgers

and they obviously really, really like it.

They're obviously very happy. It gives them a place to live,

they're secure, it gives them refuge.

Means the school isn't going to fall down, so it's a win-win.

We're learning how to share the Britain beneath our feet with

animals like these badgers, who build their whole world underground.

But it's extraordinary to think that there might have been a time

when every one of us had to look underground to survive.

I've come to the outskirts of Edinburgh to uncover

a place that belongs to a secretive and sinister era.

This is an old BBC studio that was kitted out over 50 years ago.

And it's interesting because in all that time,

it's never ever been used as a studio before, until today.

And it's just as well, because its sole function was to relay

some pretty devastating information.

RECORDING: 'This is the wartime broadcasting service.

'This country has been attacked with nuclear weapons.

'Communications have been severely disrupted and the number

'of casualties and the extent of the damage are not yet known.

'We shall bring you further information as soon as possible.

'Meanwhile, stay tuned to this wavelength, stay calm,

'and stay in your own house.'

Listening to that today,

it almost feels inconceivable that we got ourselves

into that situation.

Can you imagine hearing information like that today, how you'd feel?

When this place was set up, the government wasn't being paranoid.

In the 1950 and '60s, Russia and the West were on the brink

of nuclear war.

During the Cuban Missile Crisis, we came closer than ever to

annihilation.

JFK: 'It shall be the policy of this nation to regard any nuclear missile

'launched from Cuba against any nation in the western hemisphere

'as an attack by the Soviet Union on the United States.'

And in this tense political atmosphere,

Barnton Bunker came about.

A top-secret complex to be occupied in the event of an all-out

nuclear attack.

Today, a team of dedicated volunteers is attempting

the slow and arduous task of restoring the bunker.

Eventually, they plan to turn it into a museum.

But back in the Cold War, it was designed to withstand

the destructive blast of a nuclear bomb.

I've got hold of some amazing old documents connected to the

site from when it was built and you can see here, all round

the building, it's surrounded by ten feet of concrete and down

here you can see where the blast doors would be, which are enormous.

They weigh over a tonne each and, perhaps even more importantly,

you've got the ventilation system and this room that we're

in here are the kind of remains of that ventilation system. Over here

you've got a giant cooling unit and this bit here is the actual

filters that would have filtered out some of the radioactive particles.

The complex is enormous. 50 rooms spread over three floors.

Its generators and air filtration systems making it entirely

self-contained.

It would have held a key group of 420 people,

considered vital to keep the country running.

A cross-section of society, buried

and sealed off from the outside world, 40 feet below the surface.

Barnton Bunker in Edinburgh, was only one of a network

of 12 regional command bunkers spread across the UK.

It was from these that the country would have been run in the

event of a nuclear war, all linked by a secure telephone network.

It's startling to think that thousands of people would

have lived underground, possibly for years.

Could society really have survived in this way?

Fortunately, we never had to find out,

but places like these, like this bunker deep beneath me

that I'm standing on top of, are a really important part of our

recent history and they deserve to be restored, so that future

generations can see just how close we did come to self-annihilation.

Barnton Bunker is a chilling reminder of a world

on a permanent war footing.

But at other times,

we've gone underground for much more peaceful purposes.

The mountains of Snowdonia.

Majestic. Untamed.

And yet hidden among them

is a place we all rely on without even realising.

It's absolutely breathtaking.

There are few places in Britain where you feel

this close to nature and it's a wild refuge for many plants

and animals that would struggle to live elsewhere.

But for one particular mountain, that wilderness is only skin deep.

Mount Elidir has a secret beneath its surface.

To find out what it is, I'm actually driving into the heart

of the mountain.

It's like entering the lair of a Bond super villain.

But below this mountain is something far more useful.

Dinorwig Power Station.

These massive turbines make it one of the largest hydroelectric

power stations of its kind in the world, specifically built to

provide a rapid response in a crisis.

100 metres underground, Dean Mannion has an impressive

amount of power at his fingertips.

In terms of the number of homes, how many homes could you power?

Well, we should be able to provide enough energy for most of say

something like Manchester for about six hours now,

up to nearly six hours.

ALARM BEEPING

Suddenly, we're interrupted by an alarm.

-What did you look at on the screen?

-Here? That's flashing red now.

-So SG means...

-Spin-gen.

-Spin generator.

And that's on Ffestiniog three.

Dinorwig exists to make lots of electricity, fast.

And Dean has just received an urgent demand for more power.

These emergencies happen all the time, like at the end of a huge

sporting event on the telly, when everyone pops the kettle on.

That leads to a huge spike in demand for electricity.

The power there's just coming up.

So, 18 megawatts, 24 megawatts.

With the flick of a switch,

Dean's created enough power from the water to provide for a whole city.

There we are, we're up to 92 megawatts. There we go.

So, in a way, it is magic.

If you can imagine, we've done that with nothing but water.

Dinorwig's secret is a lake high up in the mountain.

As soon as the alarm goes off, Dean releases the water held in the lake.

It tears down the network of pipes, cascading through the mountain,

until it enters here.

The turbine hall.

The torrent is funnelled through six huge generating units.

This creates more than enough power to meet the vast demand

in just 12 seconds.

That's 30 times quicker than any normal power station.

Electricity then floods into the national grid

along underground cables.

We're about 600 meters below the lake up at the top.

So, when the water gets down to this level, it's under huge

amounts of pressure. It comes in this vast, vast pipe here,

and this is the valve, so it can either be open or closed.

At the moment it's closed, and these yellow things here,

these huge counterweights, are what open and close the valve.

But as much water passes through that valve in

90 minutes as is used by London in an entire day.

All that water powering through turbines comes with a risk attached.

This is Shushenskaya Power Station in Russia.

One day in August, 2009, workers noticed the entire building

starting to vibrate.

And then this happened.

A 1,500 tonne turbine was flung

15 metres into the air, propelled by a huge column of water.

It blasted through the building and 75 people died.

So at Dinorwig, harnessing the power of all that water safely

is an extraordinary feat of engineering.

But the water of the lake doesn't last forever.

This is the end of the process.

So, you've generated your electricity, the water's come

all the way down there and ended up here at the bottom of the mountain.

And for most hydro-electric power stations, that would be that.

But Dinorwig has one last trick.

At night, spare electricity is used to throw the whole

process into reverse.

The machinery pumps water back up to the lake at the

top of the mountain, where it sits ready to be released again.

Dinorwig is like a mountain-sized rechargeable battery

that can be used over and over.

It's power available instantly at the flick of a switch.

The power station that's buried deep inside electric mountain harnesses

water to solve that tricky problem of being able to store and then

release very quickly huge amounts of energy, and it is an amazing thought

when you think of things as mundane as making a cup of tea or charging

your mobile phone or watching TV, you're actually plugging into that.

Over the last two centuries,

we've created a whole world of connections underground.

Pipelines, water mains, power and superhighways.

All essential to keep the country running.

And in our busiest city,

we've long relied on the world below our feet to keep people on the move.

London's Tube network has over 110 miles of tunnels.

During rush hour alone,

two million people go to work on the underground.

Now, that is enough to repopulate Birmingham twice over.

But every year, the underground is getting even more

crammed as more and more people head for the capital.

To ease the inevitable congestion,

a new network is being built under the streets of London.

It's called Crossrail and, unlike the Tube, it's a full-sized railway.

But there is a problem, because the engineers,

when building this, aren't starting with a blank canvas.

Beneath the surface, London is a very, very busy place.

The first underground railway arrived in 1863.

It linked Paddington in the west, to Farringdon in the east.

More lines followed in quick succession to keep

the population of the booming city moving.

And today, this is what the real Tube map of London looks like.

But beneath the surface, it's even more complex.

Foundations.

Underground stations.

And a web of tunnels all jostle for space.

This is about to be joined by the tunnels of Crossrail.

The biggest construction project in Europe, with a price tag to match.

£15 billion.

But how can you build something so massive

without hitting anything else down here?

I'm travelling along a section of the new Crossrail tunnel,

somewhere beneath the streets of east London.

Ahead of me is the technology that makes the whole project possible.

This appears to be a construction site,

but I've actually climbed inside the bowels of one gigantic machine.

This is a tunnel boring machine,

or TBM as it's known around these parts.

It doesn't really look like a machine at all. It resembles

much more a factory or a production line, lots of different parts

doing lots of different jobs. It's absolutely enormous.

They've given it a name, they've called it Ellie.

Ellie is so big, she has to be assembled beneath the surface.

She's one of eight tunnelling machines.

Completed, each is over 100 metres long

and weighs over 1,000 tonnes.

She tears her way through London with this, a huge cutting disc.

It chews through the earth

with enough force to lift 600 London buses.

Just imagine the damage this could do if you took a wrong turn.

And yet the controls are extremely delicate.

Reginald Swift is Ellie's driver.

He uses a guidance system to keep the machine on track.

There's a GPS system at the back of the machine,

which records where we've been, where we're heading to.

At the moment, we are two millimetres offline.

Two millimetres offline, I can't believe it!

-Is that OK, two millimetres?

-That's pretty good, yeah.

And how fast are we going?

Speed wise, depending on the ground conditions, anything from,

30 millimetres a minute to 100 millimetres a minute,

depending on the ground conditions.

So, 100 millimetres, that's your top speed?

-That's your land speed record?

-That's the top speed.

-OK.

But what amazes me is the fact that, you know, you have to drill

under London where there's lots of structures, lots of tunnels,

lots of things already there, so how close can you go to these safely?

We've been within 300 millimetres,

one foot off, I think, the Northern Line at one time.

-A foot off the Northern Line?

-Yeah, one of them anyway.

That's incredibly close.

It's amazing that something

so big can tunnel through the ground without damaging anything around it.

And as Ellie heaves her way through the ground,

she leaves the completed tunnel behind her.

They're just getting ready to install some of these huge concrete

panels that you can see, which line the tunnel to give it strength.

It's an amazing process. They've got this huge robot,

that sucks the panels up and then sticks them onto the wall.

The accuracy of all of this is stunning. Millimetre precision.

So, they've completed a whole ring now, which lines the tunnel.

Without these rings, the whole tunnel could collapse

in on itself, almost as quickly as it was built.

Bad for the tunnel and catastrophic for anything that sits above.

In Egypt, a TBM like Ellie was tunnelling beneath the streets of

Cairo when just one single concrete panel of the tunnel lining gave way.

The result? A 20-metre hole in the middle of the road.

But Crossrail's engineers face even greater challenges than just

building tunnels.

Crossrail also requires stations.

Huge underground labyrinths with concourses, platforms,

connecting tunnels, escalators and ventilation shafts.

Building all this means breaking out of the safety of the tunnel's

concrete ring and digging out into unsupported mud and clay.

A particularly risky operation.

To see how difficult building a new station really is,

I've come to the Crossrail site at Farringdon.

When completed, 140 trains per hour will pass through here,

making it one of the busiest stations in the country.

It calls for a huge amount of work, which is going on

at the bottom of this hole.

Nisrine Chartouny is the engineer in charge.

Key to her work is the concrete rings I saw being inserted earlier.

-These rings are sacrificial rings.

-Sacrificial rings?

Sacrificial, so they serve a purpose in life, they're only here

temporarily, and then we take them out and we actually enlarge

the area around these rings to make a platform tunnel which is

11 metre in diameter, versus the six metre that we have now.

Removing the protective rings means there's now nothing

supporting the tonnes of mud and clay above.

The crumbling clay needs to be sprayed with concrete.

It's precise work that has to be done quickly.

We follow this spray concrete lining method, so you do it in three

phases, and it's always staggered, so you start with the top,

the middle and the bottom section

and this way you control ground movement.

It's all about controlling ground movement on the surface.

Without this ingenious technique, the busy streets of Farringdon

would start to sink.

The concrete sets hard into a solid layer

and acts just like the rings of the TBM.

And that keeps everything above ground exactly where it should be.

Back on the surface, it is almost hard to believe that

a project of that scale is going on below me, right where I'm standing.

It is almost as if they're doing it in secret, when nobody's looking.

It's that combination of brute force, of precision and elegance

that makes this a testament to the ingenuity of modern engineering.

When Crossrail opens in 2016 and an estimated 200 million Londoners

start to use it every year, we'll be more reliant than ever

on what goes on hidden beneath the streets.

Travelling around Britain making this programme, you start

to understand our familiar landscape in a completely different way.

So much of what we take for granted in our modern world would be

inconceivable without what happens below the earth.

I've discovered how the tallest building in Britain can

stand on the softest ground.

How every time we fly on holiday,

we rely on an underground pipeline that helped us win the war.

And I found some of the country's most spectacular landscapes

hidden underground.

A remarkable range of vibrant connections

and networks hidden below the familiar world we know so well.

Quite simply,

Britain would be impossible without the wonders beneath our feet.