Esther McVey has been forced to issue an embarrassing apology to MPs after a public row with Whitehall's spending watchdog.
The Work and Pensions Secretary said she had "inadvertently misled" the Commons by claiming that the National Audit Office (NAO) had called for the roll-out of the Universal Credit benefit to be accelerated.
But she defended her claim that a highly critical NAO report had failed to take into account recent changes made to the flagship benefit.
In a highly unusual step, the head of the NAO publicly rebuked the Cabinet minister over her response to its report.
'Incorrect and unproven'
In an open letter to Ms McVey, Auditor General Sir Amyas Morse said elements of her statement to Parliament on the report were incorrect and unproven.
He said it was "odd" that she had told MPs that the NAO report did not take into account the impact of recent changes to the administration of the welfare benefit, when it had in fact been "fully agreed" by senior officials at the Department for Work and Pensions only days earlier.
A Downing Street source said Prime Minister Theresa May continues to have full confidence in Ms McVey as Work and Pensions Secretary.
In its report on June 15, the NAO highlighted the hardship caused to claimants by delays in receiving payments under UC.
It concluded that the new system - being gradually introduced to replace a number of benefits - was "not value for money now, and that its future value for money is unproven".
Quizzed about the report's findings in the House of Commons on July 2, Ms McVey told MPs it was "unfortunate that the NAO was unable to take into account the significant changes recently implemented in Universal Credit" which addressed "many of the concerns" raised in its report.
Despite the report's recommendation that the programme should not be expanded until it was clear it could cope with additional claimants, Ms McVey said the NAO had expressed concern that UC was "rolling out too slowly" and should "continue at a faster rate".
In his letter, Sir Amyas told Ms McVey: "Our report was fully agreed with senior officials in your Department. It is based on the most accurate and up-to-date information from your Department. Your Department confirmed this to me in writing on Wednesday June 6 and we then reached final agreement on the report on Friday June 8.
"It is odd that by Friday June 15 you felt able to say that the NAO 'did not take into account the impact of our recent changes'.
"You reiterated these statements on July 2 but we have seen no evidence of such impacts nor fresh information."
Sir Amyas added: "Your statement on July 2 that the NAO was concerned Universal Credit is currently 'rolling out too slowly' and needs to 'continue at a faster rate' is also not correct."
Ms McVey returned to the Commons on Wednesday to issue her apology.
"I mistakenly said that the NAO had asked for the rollout of Universal Credit to continue at a faster rate and to be speeded up.
"In fact, the NAO did not say that."
She added: "What I meant to say was that the NAO had said that there was no practical alternative to continuing with Universal Credit."
But she stood by her claim that the NAO had not been able to examine the impact of recent changes.
"The impact of these changes are still being felt and therefore, by definition, couldn't have been fully taken into account by the NAO report," she told MPs
Shadow work and pensions secretary Margaret Greenwood said Ms McVey was either "incompetent" or had lied to MPs and should quit.
She said: "The NAO report is damning about the roll-out of Universal Credit, the Government's flagship welfare programme.
"If she didn't read it properly, that's incompetence. If she did read it properly and knowingly misled Parliament, then she should resign."