Crossrail, London's £14.8bn rail programme, is approaching its halfway mark. Mark Odell reports on the magnitude of an undertaking that will connect the east and west of the city with a line that includes 21km of twin-bore tunnels dug beneath the capital.
Filmed by Steve Ager and Petros Gioumpasis. Additional footage courtesy of Crossrail. Edited by Richard Topping and Darius G Laws. Produced by Seb Morton-Clark.