Those who evoke the glory of London 2012 talk about the ear-splitting cheers of thousands watching athletes compete in the gleaming structures of the Olympic Park. But in one area of continued British success, the triumph is coming in unnoticed. Britons can run, row, cycle, box – and, it turns out, they can tunnel.
"We were carrying out the biggest construction job in the world, in the middle of the biggest party in the world, and no one knew we were there," said Andy Mitchell, the programme director of Crossrail.
The 26 miles of tunnel being dug under the heart of the capital – picking a careful way among ancient remains, beneath prime property and past the oldest subterranean railway in the world – is restating Britain's traditional claim to be a world leader in the field.
Millions of tourists may be familiar with the warrens of the underground and the nation's favourite war film, The Great Escape, is arguably a tunnelling story, but the tunneller has been under-appreciated, agrees one of Britain's foremost practitioners, Martin Knights.
"There's a curiosity. There is a sniffy element, of it all being a dark, mysterious thing. You're likened to moles, and there's the dark, sinister aspects that have historically built up around the underground world. But it's a precise science, and the skills being honed in the UK are highly prized around the world."
Knights, a former president of the International Tunnelling and Underground Space Association, helped build the Cern tunnel under the Alps and is now off to extend Rio de Janeiro's metro system for the 2016 Olympics. Even the novices taking their first dip into tunnelling at a new training facility in Ilford are aware their skills will be in global demand.
A group on pre-employment training at the Tunnel and Underground Construction Academy has an energy more akin to X-factor hopefuls than back-to-work programmes. At the end of their three-week stint, Balfour Beatty will pick about 20 of the 40 trainees for jobs.
Apprentices practise on the latest machinery for spray-concrete-lined tunnels and learn the difficulties of building in confined spaces in a mockup tunnel. The academy draws on funding from Crossrail and the construction industry to match its immediate needs, but it hopes in the long term to become a global training centre.
Melvyn Parr, the academy's project manager, is adding a three-storey-high wheeled rig to simulate a shaft. "We'll black it out, drop Barry the dummy down, and they can practise winching and rescue." Safety is a fundamental part of the teaching, and trainees have to be ready for Parr to up the ante. "We throw in explosives, the lights go off, smoke comes in. It's not a nice place to be. A panic situation."
Most of the trainees are men, but women are increasingly prominent in the industry, said Anita Wu, 29, a chartered engineer now working on tunnelling plans for the HS2 rail link under London. She was chair of the youth wing of the British Tunnelling Association, a 700-strong network.
She got into tunnels by accident. "At university you don't do tunnels; you do buildings and bridges. You think you'll do things that everyone can see," she said. Yet "building things that people don't even think of" means "most tunnel engineers are even more passionate" about their work.
A look back over the decades backs up her theory. Under the Royal Docks, where Crossrail is expanding a Victorian tunnel opened in 1878, project manager Linda Miller points to brickwork that was only recently exposed in excavations. It was beautifully done, she said, by someone who would never have expected his handiwork to be visible.
Miller, a civil engineer whose previous jobs have included the space shuttle launchpad at Cape Canaveral, Florida, said second world war concrete repairs to bomb damage were more robust than expected. A scar has been deliberately left in the brick ceiling: "The American way is to patch things up but the Brits want to keep the history on display." Tunnelling here on the fringe of London City airport has involved searching for unexploded bombs, Japanese knotweed and the labyrinthine roots of unclaimed utility lines. Among the many cables unmarked on subterranean charts was a super-high-voltage power line and there were pipes unknown to Thames Water. "You need to go very gingerly through the first three metres. It's like CSI," Miller said.
Her team ended up pumping out 13m litres (23m pints) of water from the docks above when they realised that the original expansion plan would have led to a "catastrophic inundation". That is the joy of puzzling out what's underground, said site engineer Alex Mitchell, who came here after graduating two years ago. "You just don't know what you're going to find."
Across the £14.8bn Crossrail project, the variety of tunnelling work is obvious. Huge holes were excavated and structures added for some station boxes, such as Canary Wharf. The train tunnels connecting stations are dug by 150-metre-long boring machines, crewed by teams working through the night in hot, cramped conditions. These mobile factories dig out earth and line a concrete shell around them as they push ahead, spewing out spoil and laying track behind them. "German technology – based on British ideas in the 1970s," said Knights.
At Whitechapel, in a site squeezed discreetly off the main road, a small blue door in the hoardings leads, Tardis-like, to a shaft down to a 400-metre-long cavern. All is earth, concrete and machinery, bar a painted statue of Santa Barbara, the patron saint of tunnellers, standing in a small alcove. And here is a miracle unknown above: a virtual full-size platform tunnel, showing the scope of the trains which will deliver 30,000 commuters an hour through London by the end of the decade. At either end, machines are now spraying concrete to line the walls.
It's eerily affecting, a world away from the streets above. Colin Niccolls, the project manager, said: "I thought I'd be spending my life building car parks. Then I came down a tunnel and I thought, this is it. This is the bollocks."
For Niccolls, and the hundreds of apprentices now employed on Crossrail, work in tunnelling is expected to boom for some time to come. The Thames Tideway tunnel project to free the capital's river of sewage and the Northern line extension are on the cards. Across Britain, the budget for the high-speed rail project HS2 is swelling as more objectors demand trains pass underground. Many British tunnel workers will travel worldwide as huge new metro systems get under way in the Gulf states and South America.
In future, said Knights, tunnelling will evolve further as cities demand better use of underground space. "Not long and linear and circular; maybe complex and spherical shapes for storage. You're looking at thinking of a property with nice geology, rather than a nice view.
"Politicians and planners need to understand that the ground underneath your feet is fast becoming an asset."
Historic British tunnels of love
Thames tunnel, 1843
This was the world's first tunnel beneath a navigable river. It runs nearly 400 metres between Rotherhithe and Wapping, just 23 metres below the surface of the river at high tide. It took 18 years to complete, and was made possible by an invention of Thomas Cochrane and Marc Isambard Brunel: the tunnelling shield, an 84-ton bank of iron frames which divided the tunnel face and reduced the risk of collapses. Work was overseen by Brunel and his son, Isambard Kingdom Brunel, right.
The project went hugely over budget but It became a big tourist attraction as a foot tunnel, was converted to carry trains in 1869 and became the oldest part of the London Underground system. It is still being used by London Overground trains.
London Underground, 1863
The Metropolitan Railway opened the world's first underground railway to the public on 10 January 1863, running three miles between Paddington and Farringdon. It was largely financed by the City of London to overcome the damaging effect on business of horse-drawn congestion. The tunnels were dug just below the surface by the cut and cover method, in which a trench is dug and roofed over. It carried more than 30,000 passengers on the first day but the prime minister, Lord Palmerston, refused his invitation to the VIP opening the day before, saying that at 79 he wanted to stay above ground as long as he could.
Channel tunnel, 1994
Napoleon Bonaparte was reported to have remarked that "C'est une des grandes choses que nous devrions faire ensemble," French for "[it] is one of the great things we should do together" to a British ambassador. Margaret Thatcher and president Francois Mitterand invited private firms in 1985 to submit proposals and wBut wWork finally began in 1986, digging along a layer of chalk with 11 tunnel boring machines. The last metres were drilled out by workers on 1 December 1990 to allow a ceremony where the Brits walked through the hole to have their passports stamped "in France". The cost was double the original estimate.