The European Commission has threatened legal action against the UK, saying a test of eligibility for benefits discriminates against foreigners.

It says it is easier for UK citizens to prove their "right to reside" - a test imposed by the UK for certain benefits - than EU nationals.

The commission says it may refer the case to the European Court of Justice.

UK ministers fear taxpayers could be forced into handing out more than £2bn to EU nationals - including so-called "benefits tourists" - if the UK has to comply.

Ministers say it is a "fundamental challenge" to the UK's right to decide its own social security arrangements.