DUP threatens to pull support from Theresa May's government if she backs down over post-Brexit Irish border

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The Democratic Unionist Party has threatened to rethink its deal to prop up Theresa May in power if she compromises over the Irish border after Brexit.

Sammy Wilson, one of the DUP’s 10 MPs, said the party would not accept any moves that would see Northern Ireland “treated differently than the rest of the UK”.

The warning follows reports that further powers could be devolved to Belfast allowing rules in areas such as agriculture and energy to be aligned with the EU, rather than London.

The move is an attempt to meet the Irish government’s demand for a cast-iron guarantee there will be no return to a hard border with Northern Ireland, which it fears would be made inevitable by new trade barriers.

“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 United Kingdom, then they can’t rely on our vote,” Mr Wilson 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.”

He added: “If their support for the Union diminishes, then our support will not be there.”

It is understood that DUP MPs had met with senior government ministers to warn that any move to allow Northern Ireland to retain EU regulations would be “deeply destabilising” to the parties’ agreement.

The threat appeared to present Theresa May with the dilemma of how to do enough to prevent the Irish government blocking progress in the Brexit talks – but without losing DUP support.

The stakes could not be higher, because an Irish veto would prevent the UK moving the talks on to future trade and a two-year transitional deal at an EU summit next month

Under the controversial £1bn “cash for votes” deal, the DUP has agreed to back the Conservatives on financial matters and to deliver Brexit.

But the “confidence and supply” agreement does not cover the precise terms of the EU divorce deal – and the DUP has repeatedly insisted there can be no separate deal for Northern Ireland.

Dublin – with Brussels’ backing – has said the only way to avoid a hard land border is for Northern Ireland to remain in the EU single market and customs union.

Failing that, the Irish Government is demanding that the UK makes a written commitment to convergence on regulations, to avoid border checks.

Downing Street attempted to play down the row, saying: “We have been absolutely clear, on many occasions, about the need to protect the economic integrity of the whole of the United Kingdom.”

Earlier in the week Irish agriculture minister Michael Creed said his country’s government 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.”

But DUP MP Ian Paisley urged the Republic of Ireland to take a more “mature” approach to Brexit, adding: “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.

“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.”

The DUP will be extremely reluctant to jeopardise the deal, because – aside from the £1bn – it is desperate to prevent Jeremy Corbyn reaching No 10.

Nevertheless, the party has been spooked by the reports that British officials have suggested regulatory convergence between the North and the Republic as a way forward.

Earlier this week, the Conservative MEP Charles Tannock suggested in the European Parliament that the province could be given a second referendum on whether it should stay in the customs union or not.

UK and EU officials are expected to try to hammer out an agreement on the Irish border over the weekend, as the Prime Minister prepares for a crucial meeting with Jean-Claude Juncker, the European Commission President, on Monday.

Before that, European Council President Donald Tusk is expected to meet Irish leader Leo Varadkar in Dublin.