Welfare and Pensions Secretary Iain Duncan Smith's flagship benefit reform was savaged yesterday by senior MPs highlighting "shocking failures" that have already wasted at least £140 million.

The cross-party Commons public accounts committee (PAC) said the botched universal credit plans suffer from "alarmingly weak" management which has seen secretarial staff put in charge of purchase orders worth over £20m.

MPs said personal assistants had approved single payments of £8.7m, 22.6m and 1.1m - despite not have the authority to do so.

An IT cock-up means that at least £140m of the £425m current spend has been wasted.

Trade unionists said the problems dated back to the 1990s when the then Tory government hived off the in-house IT department in a move that it said would save cash.

Universal credit, which provides all benefits in one payment rather than the bundle of separate payments now provided, is scheduled to be implemented from 2017.

Mr Duncan Smith says the scheme will save £38 billion by 2023.

But the PAC voiced doubts about whether the project can still be fully delivered by 2017.

PAC chairwoman Margaret Hodge said: "The DWP has failed to grasp the nature and enormity of the task, failed to monitor and challenge progress regularly and, when problems arose, failed to intervene promptly."

PCS industrial officer Charles Law said: "The IT companies are still being paid even though they have failed to deliver.

"Ian Duncan Smith is also to blame - other secretaries of state have seen universal credit was a lost cause and left it alone. He's also imposed a ridiculously fast time table."