AN influential MP has questioned whether ministers are telling the truth about the government's troubled flagship benefit reforms.

Public accounts committee chairwoman Margaret Hodge described the "smoke and mirrors" over universal credit (UC) during a parliamentary debate on Monday night.

She suggested that civil service chief Sir Bob Kerslake’s account that the Treasury had not fully signed off the reforms appeared to differ from that of Employment Minister Esther McVey.

Labour claims Ms McVey has said in written parliamentary answers that the business case for UC had been approved by the Treasury.

Ms Hodge said backbenchers need a mechanism to determine "who is telling the truth" as two other senior civil servants gave her committee vague accounts of UC's progress.

Treasury permanent secretary Sir Nicholas Macpherson repeatedly dodged questions about whether it had been signed off but said there were Treasury decisions to be made "at each key milestone". 

Cabinet Secretary Sir Jeremy Heywood also told the committee that "in its current form" UC is on track.

Raising a point of order in the Commons, Labour MP Ms Hodge said: “The importance here for backbench members is we need to know who is telling the truth — the head of the civil service or the minister?

"Smoke and mirrors have been used, hundreds of millions of pounds are at stake, millions of benefit claimants will have their future at risk.”

UC — a project that will unify six different welfare payments — has been beset by problems since its launch.

More than £40 million spent on IT was written off in 2012/13, with a further £91m of software code expected to be written down in value to nil over the next five years.