Migrants are 20 per cent more likely to be claiming working tax credit than Britons, it is claimed.
Nearly 500,000 migrants are claiming the in-work benefit, a former HM Revenue and Customs official said.
Ministers have previously said they do not know how many foreigners are claiming tax credits.
Tax credits will be included in the universal credit welfare system from 2014 and the nationality of claimants will be recorded.
A Government study published last year found that British-born people were more than twice as likely to be claiming working-age benefits than immigrants.
Those figures referred to out-of-work benefits such as jobseeker’s allowance, employment and support allowance, and disability living allowance.
However, a report by Michael O’Connor, a former policy official at HMRC, suggests that migrants are more likely to be claiming working tax credit than the rest of the population.
The data shows that 14.6 per cent — or one in seven people — claiming working tax credit is a non-UK national.
It also disclosed that one in six people — or 17.6 per cent — of those claiming both working tax credit and child tax credit is a non-UK national. Tax credits were introduced by Gordon Brown to top up the incomes of the lower-paid, particularly those with children.
They are regarded by Labour as one of the party’s proudest achievements.
Douglas Carswell, the Conservative MP for Clacton, said: “If we are to attract the brightest and the best — rather than the relatively unskilled benefit migrants – we need to have an open and honest debate about the kind of immigration we currently have.
“The claim that migrants are half as likely to claim benefits as UK nationals turns out to be a myth.”
The report emerged as a group of academics warned that a target by ministers to reduce net immigration below 100,000 by 2015 is “neither a useful tool nor a measure of policy effectiveness”.
Prof John Salt and Dr Janet Dobson, of University College London, said they had “serious doubts” about the target.
In the most recent figures, the Office for National Statistics disclosed 176,000 more people entered Britain than left in the year to December 2012, ending five consecutive quarters of decline.
An HMRC spokesman said: “European Economic Area migrant workers must be resident in the UK and paying compulsory UK national insurance contributions … to claim Working Tax Credit.
“These figures show the majority of non-EU migrants who are claiming tax credits are in work.”
See on www.telegraph.co.uk