DAVID CAMERON’S drive to strip EU migrants of in-work benefits suffered a fresh setback after Denmark declared it a “red line”.

Helle Thorning-Schmidt, the centre-Left Danish Prime Minister who had been regarded as one of Mr Cameron’s closest allies on EU reform, has decided she will not back Downing Street’s plan for treaty change.

“Don’t think we will follow the Brits no matter what,” she told a public event on Friday.

She is seeking re-election against a Right-wing opposition that has backed Mr Cameron’s reform plans.

Martin Lidegaard, her foreign minister, told The Daily Telegraph: “We have made it very clear that we don’t believe that a treaty change will be realistic, and that the solutions we find will be non-discriminatory and will not disturb the free movement of Europe. That’s the red lines for the government.”

Denmark joins a handful of EU states, including Poland, Romania, Finland, Spain and Belgium, that have publicly rejected Mr Cameron’s proposals, which seek to cut migration by limiting the state-subsidy for low-paid work done by migrants.

The policy is difficult to sell because EU treaties ban discrimination on grounds of nationality in working conditions and pay – something some governments argue includes in-work benefits and tax credits. The Daily Telegraph understands Mr Cameron believes he can overcome their opposition by arguing the policy will help stem a brain drain of talented workers which is hobbling the economies of eastern Europe.

A British official confirmed: “There are countries around the EU who have got challenges with their younger working age population migrating; it’s the sort of point we’re making.”

Mr Cameron is undertaking a tour of Europe to see each leader individually ahead of a presentation to all 27 at a Brussels summit at the end of the month.