Talks between the British government and the European Union, with the heavy involvement of Irish officials, are entering a critical stage in Brussels, as the EU side seeks concrete assurances on the Border from the British.
Although there was no signal from either side about the progress of the talks last night, the DUP was sufficiently alarmed by the prospect of UK concessions on the Border to warn British prime minister Theresa May that any concession which affected Northern Ireland's relationship with the rest of the UK risked the party's support for Ms May's minority government.
In a further development, Westminster’s Brexit committee said it could not see how Britain’s commitment to keeping the Border open could be reconciled with its policy of leaving the customs union.
DUP leader Arlene Foster said she had made it clear to the British government there could be "no arrangements agreed that compromise the integrity of the UK single market and place barriers, real or perceived, to the free movement of goods, services and capital between Northern Ireland and the rest of the United Kingdom".
DUP MP Sammy Wilson said he was seeking clarification from the British government on reports that Ms May was preparing to make concessions to the EU on the Border.
"If there is any hint that in order to placate Dublin and the EU they're prepared to have Northern Ireland treated differently than the rest of the UK then they can't rely on our vote," he said.
“They have to recognise that if this is about treating Northern Ireland differently or leaving us half in the EU, dragging along behind regulations which change in Dublin, it’s not on,” Mr Wilson added.
The fears in the DUP were being interpreted in political circles as evidence that a British move was becoming more likely.
Discussions between the British and the EU will continue today and over the weekend in advance of a crucial meeting between the Ms May and European Commission president Jean-Claude Juncker on Monday at which Ms May is expected to table the British offers on the Border, the Brexit bill and citizens' rights.
Last night, Tánaiste and Minister for Foreign Affairs Simon Coveney reiterated the Irish position, saying the Government "cannot accept the re-emergence of a border on this island".
Other EU countries were fully supportive of Ireland’s position he said, and if the British were unable to supply satisfactory assurances on the future of the Border, “then this process will have to be delayed”.
Taoiseach Leo Varadkar is to hold a meeting in Dublin later today with Donald Tusk, president of the European Council, the group of EU leaders.
EU leaders will meet at a summit in Brussels in mid-December to formally decide if the negotiations can move on to the second phase as the British are requesting. However, the deadline for agreement is in reality much tighter, and senior sources say agreement in substance on the Border and other issues will have to be reached by the end of next week. Mr Varadkar is also scheduled to speak to Mr Juncker over the weekend.
Meanwhile, Westminster’s Brexit committee has said it cannot see how Britain’s commitment to keeping the Border open can be reconciled with its policy of leaving the customs union. A report to be published on Friday by the Exiting the European Union Committee, which includes MPs from the government and opposition parties, said it recognised the unique challenges Brexit poses for Ireland.
"Our report concludes that we cannot at present see how leaving the customs union and the single market can be reconciled with there being no border or infrastructure. Even by their own admission, the government's proposals are untested and speculative, so it has yet to set out how no border can in practice be maintained with the UK outside the single market and the customs union," said Labour's Hilary Benn, who chairs the committee.
The report notes statements from Mr Varadkar and Mr Coveney in recent weeks and calls on the British government to spell out its plans to avoid a hard Border after Brexit.