The DUP has poured cold water on a European Union offer of compromise on its proposals for the Irish border after Brexit.

Ahead of a summit in Austria at which Theresa May will appeal for flexibility from Brussels, the EU’s chief negotiator Michel Barnier said he was ready to come forward with a new offer on the Irish border.

In order to “de-dramatise” the main obstacle to a withdrawal deal, Mr Barnier suggested arrangements could be made to conduct the majority of checks on imports and exports away from the border itself.

He warned that time was running out, with the “moment of truth” coming at the next full EU summit in Brussels on October 18, when it would become clear whether an agreement was “in our grasp”.

But the Democratic Unionist Party, which props up Mrs May’s minority administration in Parliament, dismissed Mr Barnier’s proposals as unpalatable, because they would involve a customs border between Northern Ireland and the rest of the UK.

“It still means a border down the Irish Sea although with different kinds of checks,” said the party’s deputy leader Nigel Dodds.

“The fact is that both Theresa May and the Labour Party have said no British prime minister could accept such a concept. It is not just unionists who object.”

Brexit
Michel Barnier has said he is ready to make an improved offer on the Irish border (Niall Carson/PA)

Former shadow Northern Ireland secretary Owen Smith, a backer of the Best for Britain campaign for a second EU referendum, said Mr Dodds’ response had “sunk Barnier’s improved offer on Northern Ireland before he has even floated it”.

Wednesday’s gathering in Salzburg will be the first time EU leaders have met since Mrs May published her Chequers blueprint for Brexit in July.

It comes as supporters of a second referendum publish a blueprint setting out how MPs could force the Prime Minister to accept what they call a People’s Vote on her deal, with the option of remaining in the EU.

Despite Mrs May insisting the choice was between her deal or no deal, Treasury minister Mel Stride appeared to suggest that a second poll was still a possibility.

Mr Stride told Sky News: “When we have a firm deal on the table, I suspect that those to the right of the party – the pro-Brexit wing – will be very concerned that if that deal does not prevail, they will end up in the situation where we could have a second referendum or we could end up not leaving the EU altogether, so there is a danger of that happening if Chequers does not prevail.”

Over dinner at the Felsenreitschule – the theatre where the Von Trapp family performed before fleeing the Nazis in The Sound Of Music movie – Mrs May will set out her plan and explain why Brussels should show more flexibility to give her the support she needs.

Brexit graphic
(PA Graphics)

As part of the drive to set out the UK’s position to the EU’s leaders, she used an article in German newspaper Die Welt to explain her stance.

The Chequers blueprint – a “common rulebook” for trade in goods and “business-friendly facilitated customs arrangement” – is the only way to resolve the thorny issue of the border between Northern Ireland and Ireland, she said.

“It is profoundly in both sides’ economic interest, it respects the integrity of the single market and, crucially, no-one else has come up with a proposal that could command cross-community support in Northern Ireland that is the only true foundation for stability there.”

Mrs May said: “To come to a successful conclusion, just as the UK has evolved its position, the EU will need to do the same.

“Neither side can demand the unacceptable of the other, such as an external customs border between different parts of the United Kingdom – which no other country would accept if they were in the same situation – or the UK seeking the rights of EU membership without the obligations.”

Mrs May is expected to use the Salzburg summit to hold formal face-to-face talks with Belgian premier Charles Michel on Wednesday and Ireland’s Leo Varadkar and European Council president Donald Tusk on Thursday.

She may talk to other leaders in the margins of the summit in an effort to win backing for a plan which has met fierce resistance from within the ranks of her own Conservative Party.

Attention had been increasingly focused on the prospect of a special summit in November to finalise an agreement, but Mr Barnier said it should be clear before then whether a deal was possible.

European Council president Donald Tusk said EU leaders should discuss arrangements for the “final phase” of the Brexit talks “including the possibility of calling another European Council in November”.

In a letter to leaders ahead of the Salzburg meeting he called on them to work on “limiting the damage” caused by Brexit.

“Unfortunately, a no-deal scenario is still quite possible. But if we all act responsibly, we can avoid a catastrophe,” he said.