The UK government has consistently declined to provide evidence to support its claims about “benefit tourism”, the European Commission has said.
Jonathan Todd, a spokesman for Employment Commissioner László Andor, told the BBC that the Commission had been asking for about three years.
He “sincerely hoped” that ministers would set the record straight, he said.
But No 10 said there was “widespread and understandable concern” over people coming to the UK to access benefits.
The Commission’s intervention follows its publication of a report claiming that jobless EU migrants make up less than 5% of those claiming social benefits in most of the EU member states studied.