Sammy Wilson: DUP is not bluffing over threat to Theresa May

His warning comes as former UUP leader Lord Empey said the DUP – which is propping up the minority Tory administration – has “overestimated its influence” at Westminster.

In a move which ratchets up the pressure on Downing Street, Arlene Foster’s party say they are ready to block the budget and potentially topple the prime minister unless they receive sufficient reassurances that there will be no Irish Sea border post-Brexit.

In what Mr Wilson dubbed a warning shot, the DUP abstained - rather than backing the government - in a vote on the agricultural bill on Wednesday.

While some Tory MPs have said they believe the DUP is “bluffing” about withholding its support, Mr Wilson yesterday warned: “Do not take our votes for granted”.

The East Antrim MP told the News Letter: “We are genuinely alarmed by what we have been hearing about the discussions surrounding Brexit and the backstop.

“We have told the government that if they are going to break their promises to us then we don’t feel bound by any agreement we have with them. We have sent a very clear and strong signal and they now have to decide how to respond.”

Mr Wilson said his party had “a duty to use whatever influence we have” to protect Northern Ireland’s place within the Union.

And while he said he was unsure if the party’s radical strategy would succeed, the MP added: “We don’t want to look back and think if we had sent a clearer signal to government things would have turned out differently.”

Despite the DUP’s warnings that it will use its leverage to ensure NI is not treated differently to the rest of the UK after Brexit, UUP peer Lord Empey appeared sceptical that the gambit would have the desired outcome.

The former Ulster Unionist leader said the DUP had made a “fundamental error” in backing the government’s backstop arrangement last December.

He told the News Letter: “The DUP have not played their hand well. They should never have agreed to the backstop, even in its amended form. The EU have used it as a battering ram for last 10 months and continue to do so.”

When asked if he felt the DUP would follow through with its threats to withhold support from the government, Lord Empey replied: “I am not saying they are bluffing, but I think they have boxed themselves into a corner.

“They campaigned to get us out of the EU and it is clear they had no plan as to how it was to be done. They are now running around like headless chickens at the last minute trying to prevent themselves being sold down the river. They have left us all in a very unprepared and precarious position.

“The DUP have overestimated their influence and misjudged the situation. They were swaggering around telling everyone how much influence they have. Well, we will see how much influence they have when push comes to shove.”

However, TUV leader Jim Allister said it is “imperative” that Mrs Foster’s party “stands its ground”, adding: “My profound differences with the DUP are well known but on the seminal issue of Brexit it is imperative, both in the national interest and Northern Ireland’s interest, that the flagitious EU backstop – and the Government’s flirtation with it – is thwarted.

“I encourage the DUP to stand firm. To do otherwise is to betray not just Brexit but our position as an integral part of the UK.”

Meanwhile, the DUP has stepped up warnings to Mrs May not to compromise over the Northern Ireland border in her efforts to secure a Brexit deal.

Following three days of talks with key figures in Brussels, Mrs Foster said the prime minister could not in “good conscience” accept the proposals currently on the table from the EU.

Her intervention came as Mrs May met key Cabinet ministers in Downing Street to brief them on the progress in the Brexit negotiations.

The PM was reported to have played down the prospects of a breakthrough at next week’s EU summit in Brussels, billed as the “moment of truth” by European Council president Donald Tusk.

In a statement Mrs Foster said the EU plan would effectively mean imposing a trade barrier between the Northern Ireland and the rest of the UK.

“The prime minister is a unionist. Many of her cabinet colleagues have assured me of their unionism,” she said.

“Therefore, they could not in good conscience recommend a deal which places a trade barrier on United Kingdom businesses moving goods from one part of the kingdom to another.”