Iain Duncan Smith faced embarrassment after he was chided by the statistics watchdog over claims he made trumpeting the success of a Government key welfare reform.
The Work and Pensions Secretary asserted that plans for a £26,000-a-year cap on the amount benefit claims could receive had already spurred 8,000 unemployed people to find jobs.
But the UK Statistics Authority said his claim was “unsupported” by his own department's figures.
Its ruling followed a complaint from the TUC. Its general secretary, Frances O'Grady, said: “Only people with weak arguments need to make up statistics.”
The authority said the figures used to justify Mr Duncan Smith's statement had explicitly warned that they were “not intended to show the additional numbers entering work as a direct result of the contact” with staff from the Department for Work and Pensions (DWP).
Andrew Dilnot, the authority's chairman, protested that the department had not “fully complied” with the code of practice on official statistics and wrote to the minister to seek “further assurance” that statistics would in future be handled correctly.
It was not the first time Mr Duncan Smith has fallen foul of the statistics watchdog, which rebuked him last year over “weaknesses” in data used in a document on benefit claims by immigrants.
A DWP spokeswoman said: “The Secretary of State has long held the position that the benefit cap would have an impact on the behaviour of claimants.
She added: ”DWP staff and claimants are telling us the cap is impacting behaviour and leading to those affected finally entering the world of work.“
But Liam Byrne, the shadow Work and Pensions Secretary, said: ”Iain Duncan Smith is living in la-la land. His ideas don't work so he is now literally making up stories.“
Oxfam's Katherine Trebeck, policy and advocacy manager for the charity's UK poverty programme, said: ”Not content with using rhetoric to stigmatise poor people, the Government has now been caught misrepresenting the figures. This is beyond the pale.“