RAIL union leader Manuel Cortes has demanded a parliamentary inquiry into the “badly delayed and over budget” running of the Crossrail project.

The TSSA general secretary made the call in a letter to Huw Merriman, who is the incoming chairman of the transport select committee.

In the letter, he asks the committee to “consider an inquiry into why this vital piece of infrastructure, which would increase rail capacity by 10 per cent across the capital, is so badly delayed and over budget.”

He asserted that his union’s members need reassurance from companies tasked with completing the project.

Mr Cortes also demanded clarity on whether “private contractors, who have caused the delay to this much needed scheme, will foot the bill and not long-suffering Londoners.”

Mr Merriman took over as committee chair on Wednesday, replacing outgoing Labour MP Lilian Greenwood, as broader questions are raised over the effectiveness of planning on the Crossrail project.

Earlier this month, it was revealed that the route, which goes from London to Reading and Shenfield, is not due to start running until 2021, due to train-testing issues.

The project is now estimated to be finished exactly three years later than companies originally planned.