Home Secretary Theresa May, who has said Britain will play no part in an EU scheme to relocate migrants coming across the Mediterranean

Britain's row with Europe escalated last night as Brussels threatened retaliation for the Government refusing to accept a strict quota of asylum seekers.

Theresa May drew a red-line by insisting the UK would play no formal part in an EU scheme to relocate the thousands of migrants who have made perilous boat journeys across the Mediterranean.

The Home Secretary also insisted there should be no bar on forcibly sending failed asylum claimants home – pointing out many of them were ‘economic migrants’.

The European Commission conceded that it could not force Britain to play a part in any of its resettlement schemes because the UK has a long-standing opt-out.

But, in what was seen as a shot across Britain’s bows, the Commission said it was considering changing the ‘legal parameters’ of the so-called Dublin Convention to ‘achieve a fairer distribution of asylum seekers in Europe’.

Under Dublin, migrants must claim asylum in the first EU country they arrive in. Any who subsequently make a second claim in another member state can be sent back.

The Commission’s threat means Britain could be left unable to remove asylum seekers who had already tried their luck in countries such as Greece, Italy or France.

Diplomatic sources said the EU was trying to ‘rattle Britain’s cage’, but they insisted any changes to Dublin would have far less impact than if Mrs May had signed up to the quota system – which could have led to Britain taking up to 60,000 asylum claimants a year.

Since 2003, the Home Office has been removing only 1,000 a year under the Dublin Convention. One source said: ‘If the choice is between Dublin and having to take an unspecified and unpredictable quota decided by the EU, I will go for ditching Dublin.’

The row is heightening tensions between the Government and EU at a time when David Cameron is beginning negotiations over an in/out EU referendum.

European Commission vice-president Frans Timmermans said: ‘It is not acceptable for people around the EU to say, “Yes, stop people dying in the Mediterranean”, and at the same time remain silent when the question is raised, “What should happen to these people?”.’

But Mrs May said while the situation in the Med was ‘intolerable’, the quota system would only encourage more people to make the journey. She emphatically rejected an assurance given by the EU that no migrants intercepted at sea ‘will be sent back against their will’.

Britain disputes the claim that it does not voluntarily play its part. Last year, it gave asylum to 14,065 people, putting the country fifth after Germany, on 47,555.

Several large EU states gave asylum to only a few hundred each. Spain accepted 1,600, Poland 740, Ireland 495, Portugal 40 and Luxembourg 135.

Sailors from HMS Bulwark help to rescue migrants who became stranded in the Mediterranean on unsuitable boats

The European Commission conceded that it could not force Britain to play a part in any of its resettlement schemes because the UK has a long-standing opt-out

Tory MEP Timothy Kirkhope said: ‘True solidarity cannot be created through compulsion alone, and binding quotas oversimplify the solution for such a complex situation.

‘There needs to be a clear differentiation between economic migrants and those seeking genuine asylum in order for Europe’s asylum approach to work effectively and efficiently.’

Senior immigration sources said the Dublin Convention had not been working for Britain.

The courts have ruled that, on human rights grounds, it is unfair to send asylum seekers back to Greece because the prisons are in a poor state.

Meanwhile, the French and Italian authorities have been ‘conveniently’ failing to fingerprint asylum seekers. This makes it impossible for Britain to prove that is where they first made their claim.