A damning report from the Public Accounts Committee has slammed the Department for Transport, Transport for London and Crossrail for not clearly identifying the reasons for busting the budget by £2.8bn.

The committee fears that even more money will be needed to finish the project and its revised opening date of 2020 will not be hit.

It said: “New train services were due to start in December 2018 but have been badly delayed.

“Until a revised opening schedule has been agreed, we are not convinced that new services will start to run in 2020 as now hoped, nor that the additional £2.8 billion of funding provided will be enough.”

The committee is now demanding a letter from the DfT, Crossrail and Transport for London by the end of this month “clearly articulating” who is responsible for the project problems.

Chair Meg Hillier added the letter “must and set out clearly what consequences there have been for well-rewarded officials whose costly failures are paid for by taxpayers.”

The Enquirer has previously reported on handsome performance bonuses paid to project chiefs.

The committee attacked previous managers for ignoring warning signs that the project was in trouble.

Hillier said: “It is clear that the delivery deadline of December 2018 had been unrealistic for some time.

“But the Department for Transport, Transport for London and Crossrail Limited continued to put a positive face on the programme long after mounting evidence should have prompted changes.

“Wishful thinking is no basis for spending public money and there remain serious risks to delivering this programme, with a revised schedule and costings for completing the work still to be agreed.

“It is unacceptable that Parliament and the public still do not know the root causes of the failures that beset this project.

“Nor will we accept the Department and Crossrail Limited’s description of these serious problems as ‘systems failures’.”