Without seeing the detailed research, it is difficult to say, but there is some more detail in the BBC's report here, headlined "Benefits being claimed by more than 370,00 migrants." It says that 371,000 people, out of a total of 5.5 million, who are claiming working-age benefits, were non-UK nationals when they first registered for a National Insurance number; of these 258,000 were from outside the European Economic Area. Of this latter group, 54% are now British nationals, so presumably the rest are not.
Meanwhile, for comparison, we can also look at the Labour Force Survey. This says that, of the total number of people in work (about 29 million), some 4 million were born abroad. Of these 2.7 million were born outside the EEA. And of these, 1.3 million are not (yet) British citizens.
So, summing up these numbers in very rough percentages:
- migrants represent about 13% of all workers, but only 7% percent of out-of-work claimants;
- migrants from outside the EEA represent about 9-10% of all workers, but about 5% of out-of-work claimants
- foreign nationals from outside the EEA represent about 4.5% of all workers, but a little over 2% of out-of-work benefit claimants.
This is hardly surprising, for structural and demographic reasons:
- many migrants come here primarily to work, so are likely to be over-represented in the workforce relative to out-of-work benefits
- initially migrants are less likely to be entitled to benefits; it takes time to build up entitlement to contributory benefits like Jobseekers' Allowance, and to get means-tested benefits you usually need to establish permanent residency
- their age structure and other demographics probably make them less likely to claim benefits