London's Super Tunnel

Building a brand new underground railway is never easy, but building one underneath the streets of one of the world's biggest and busiest cities is especially tough. The engineers building London's new underground "Crossrail" have to make sure that listed buildings don't crack, the tubes keep running, the City stays in business and that a consignment of priceless vintage cars doesn't fall down a grout shaft in Mayfair. Most dramatically, they must drive one of their gigantic 1000-tonne tunnel boring machines through a tiny gap in the congested underbelly of Tottenham Court Road station without the passengers on the platforms below knowing they are there.

In this second instalment of the three-part series, the engineers building London's brand new underground railway, "Crossrail" must take on a Great British obsession - building train tunnels under water. Linda Miller, an American engineer more used to building space launch complexes at Cape Canaveral, finds rebuilding a Victorian tunnel under the Royal Docks in London's east end more complicated than originally thought. A British tunnelling dynasty - the Berminghams - follow in the footsteps of the original father-son team of Marc and Isambard Kingdom Brunel to build the latest tunnel under the river Thames, and a young engineer goes through an important rite of passage

Building the UK's newest underground railway is a big job: it's big money, big trains - and it needs big stations. In this final part of the three-part series, engineers must put together the giant jigsaw that will become a cathedral-sized station at Canary Wharf. It's so big they have to build it in a dock and underwater. Its architect designed roof is so complicated it comes in a kit of over 2500 pieces. As engineers carve out the underground caverns that will become the new stations, they hit on some gruesome discoveries of London's past.