The Work and Pensions Secretary was today accused of misrepresenting government statistics in order to claim his cap on benefits was driving people to find work.
The Department for Work and Pensions(DWP) released figures yesterday showing the number of people expected to be hit by the cap had fallen from 56,000 to 40,000. Iain Duncan Smith hailed the figures, saying the cap had provided a "strong incentive" for people to look for jobs.
However, Jonathan Portes, the National Institute of Economic and Social Research and a former chief economist at the DWP, said "there was no evidence at all" that the cap had affected people's behaviour.
Mr Portes told the BBC Radio 4 Today programme: "It may be that the benefit cap has indeed had the effect that Iain Duncan Smith would like it to have.
"That is perfectly possible but without doing the analysis - and it has not been done - you simply cannot say that and you shouldn't say it.
"This is, I am afraid, a consistent pattern of trying to draw out of the statistics things which they simply don't show."