Government figures showing 371,000 immigrants were on benefits were rushed out by ministers with insufficient regard for "weaknesses" in the data, the independent statistics watchdog has complained.
In a strongly worded letter to Iain Duncan Smith the head of the UK Statistics Authority condemned the mishandling of the research by his department.
Despite being "highly vulnerable to misinterpretation", the claims were given to the media without the safeguards demanded for official statistics, Sir Michael Scholar said.
By issuing the figures to the press as a "research paper", the Department for Work and Pensions (DWP) had bypassed the need to meet the usual code of conduct, he added.
Sir Michael said the move had also allowed ministers to issue a "political commentary". He called for assurances that any future release would be treated more carefully.
Mr Duncan Smith said he would consult with the watchdog over how such information would be published in future but that at present there were "no plans at present to repeat this analysis".