London's Mayor Sadiq Khan must shoulder more blame for the Crossrail delays and Transport for London's financial crisis, north London MP Theresa Villiers has said.
It comes as the board for the multi-billion pound Crossrail project finally announced a potential opening date for the rail line as October next year.
However, transport bosses have given themselves a six-month period, meaning Crossrail may not be running until March 2021.
The project was supposed to open in December last year, with TfL estimating it will lose £600m in income over the next five years because of the delay.
TfL is also facing a £500m budget deficit - with essential schemes across London halted because of a lack of funding.
Chipping Barnet MP Theresa Villiers, who used to be a Crossrail Minister, accused Mr Khan of losing control over TfL's finances.
Speaking on ITV's The Late Debate, she said: "When I was in charge it seemed to be going very well and certainly I would routinely get the officials in to say 'how's it going, where are the risks?'
"it's a concern that the Mayor has overseen a serious postponement and I think it's systematic of his mismanagement of the transport system in London."
The Conservative MP added: "The is the Mayor who has mismanaged the TfL budget, spent more than he can afford. He's thrown money at things like the pedestrianisation of Oxford Street, which isn't happening.
"He's thrown money at many cycle schemes which are unpopular locally and probably unnecessary."
Earlier this week, the London Assembly Transport Committee released a report calling for TfL Commissioner Mike Brown to stand down over the delay.
It also accused Mr Brown of withholding information about problems facing the project from City Hall.
Both TfL and the Mayor's Office have rejected this finding in the report. Benthal Green and Bow MP Rushanara Ali defended the Mayor's record, and said the Government must take responsibility for cutting funding.
The Labour MP said: "What we've recently found is that very important information has actually been withheld from the Mayor. That's not acceptable and the delays need to be sorted out.
"This is a joint responsibility between TfL and the Government and the failure is in terms of resources and oversight by national Government." The Department for Tranpsort (DfT) jointly owns the company in charge of building Crossrail with TfL.
Earlier this year, the DfT was accused for having a "laissez-faire attitude" and being over-optimistic over the programme's opening date in a Commons report.
Liberal Democrat and Kingston MP Ed Davey said: "Why aren't they sitting down together, sorting this out together, bringing the Department for Transport's officials together with TfL.
"They should be sitting down together. I blame both of them."