Going behind the scenes of the world's oldest, largest and busiest underground train network as it undergoes the biggest overhaul in its history.

The number of passengers on the Tube has gone up by a third in the last ten years. David Waboso, London Underground's head of upgrades, thinks he has the answer. But new trains on the Victoria Line keep letting him down because of a problem with the doors - and a newly-installed signal fails, causing huge delays.

At Tottenham Court Road station, supervisor Barry Griffiths is keeping the crowds moving - in the midst of huge rebuilding works making the station six times bigger. But will his customers be impressed with the results? Show less