The United Kingdom is heading for a no deal Brexit, the Chief Whip of the Democratic Unionist Party (DUP) has warned.

Jeffrey Donaldson said on Tuesday that an agreement with the EU looked unlikely, after Ireland made clear it would never allow the UK to a end proposed “backstop” unilaterally.

Brexit talks have been deadlocked over the so-called backstop – the fallback position that would be activated if a future EU-UK trade deal does not produce a solution that would prevent a hard border between Ireland and Northern Ireland.

As Theresa May is reliant on the DUP for her Commons majority, losing its support would make the job of pushing her Brexit deal through parliament even harder.

May convened a meeting of her Cabinet on Tuesday morning amid reports that Brexit Secretary Dominic Raab and other ministers were pushing for the UK to be able to quit any backstop with a few months’ notice.

Ireland’s Prime Minister Leo Varadkar yesterday told the PM this would be unacceptable to the EU.

In a phone call on Monday, Varadkar said while he would consider proposals for a “review mechanism” that could dissolve the safety net – but the UK would not be allowed to trigger it alone.

Under the EU’s proposal, Northern Ireland would remain in the customs union and in the single market for goods.

But this has been rejected by London, as it would see customs checks take place between Northern Ireland and the rest of the UK.

It has been reported that May is close to striking a backstop deal with Brussels which would keep the entire UK in a customs union.

The problem for the prime minister is a significant number of Tory MPs are not prepared to accept any backstop that does not have a time-limit. While the EU has refused to accept a backstop that does have a time-limit.

John McDonnell last night confirmed Labour would not support a temporary customs union with the EU. He told the BBC the party would only support the UK remaining in in a customs union if it was permanent.