Disaster struck when Crossrail engineers working at a substation in east London flicked a switch. Instead of powering up the capital’s newest Tube line to begin testing trains, the Pudding Mill Lane substation exploded. The shockwaves from last November’s accident are still being felt. Crossrail’s recent admission that its opening will be delayed by nine months owes much to the blast, which pushed back testing of the new Bombardier trains by months.

That delay will eat into the budget of Transport for London (TfL), which is funding construction of the line together with the Department for Transport. In July, Crossrail admitted it needed a further £590m, taking the total cost of the project to £15.4bn. The budget shortfall is expected to rise yet again, to