The UK Government will not be able to rely on the votes of the DUP in parliament for any Brexit deal that treats Northern Ireland differently from the rest of the UK, one of the party's MPs has warned.
Sammy Wilson's warning came amid pressure from the Irish Government for the UK to agree a special arrangement under which Northern Ireland would continue to observe the rules of the EU's customs union to avoid a hard border with the Republic.
Border issues appear to be the biggest remaining obstacle to a green light for talks on post-Brexit trade at an EU summit next month, after reports that the UK has agreed the broad terms of a financial settlement which would see it pay up to £50 billion over a number of years.
Both governments have voiced their determination to avoid a return to checkpoints and border posts, but Irish Agriculture Minister Michael Creed said no solutions had been offered by the UK government.
The UK's Department for Exiting the EU (DExEU) refused to comment on a report in The Times that British negotiators had put forward a proposal to devolve powers to Northern Ireland to enable "customs convergence" in areas such as agriculture and energy in an attempt to break the deadlock.
The paper quoted sources that say there had been "movement" on the issue and confidence was growing that agreement could be reached in time for next month's summit in Brussels.
Responding to the report, Mr Wilson said his party will be "making clear to the government we have a confidence and supply arrangement with them", under which the minority Conservative administration relies on the support of the 10 DUP MPs to ensure its survival.
The East Antrim MP told the BBC: "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.
"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."
Theresa May is desperately hoping EU leaders will give the go-ahead for the second phase of the negotiations - including talks on a free trade deal - to begin at the European Council summit on December 14-15.
She is due to travel to Brussels on Monday for talks with European Commission president Jean-Claude Juncker in the hope of securing a declaration that "sufficient progress" has been made on divorce issues like the financial settlement and the Irish border.
The leaders of the remaining 27 EU states, including Leo Varadkar, have a veto on triggering the second phase of talks, meaning Mrs May must be sure of support for progress to be made.
However, appearing on BBC2's Newsnight yesterday, Mr Creed said they had yet to see a workable solution from the UK.
He said that having ruled out an Irish proposal for Northern Ireland to remain part of the single market and the customs union, it was up to the British to say how they could get round the need for border checks.
"If the UK has clearly said no to a single market and customs union, it is clearly incumbent on the British Government to articulate a way forward that enables us to have an invisible, seamless border which they have said they want," he said.
"We need political solutions now and we are not getting them from the UK Government."
DUP MP Ian Paisley urged the Republic of Ireland to take a more "mature" approach to Brexit.
"If the Republic of Ireland is going to keep shouting at our border and telling us that it is all doom and gloom and we are not going to get a proper relationship, that interferes in the negotiation process," he told RTÉ.
"All of us, every constituent part, Northern Ireland, Scotland, Wales and England, are leaving the EU.
"Don't undermine our position and our sovereign integrity."