Sammy Wilson last night warned Theresa May that the DUP would bring her government down if she leaves Northern Ireland “languishing in the stifling embrace of the EU”.
The 10 DUP MPs who prop up the Conservative government are preparing to vote against Mrs May’s Budget if the Prime Minister breaks their Brexit red lines.
The radical move is one of the options being considered by the DUP if attempts to nail down a deal with Brussels include any proposals that would leave Northern Ireland being treated differently to the rest of the UK, it is understood.
In a move seen by some as a warning shot, DUP MPs failed to back the Government in voting against a Labour amendment to an Agriculture Bill outlining post-Brexit reforms last night.
Despite their abstention, it was still defeated by 59 votes.
But losing DUP support in the Commons would mean possible defeat for the Government on the Budget and a no-confidence vote.
And in a Daily Telegraph article, DUP MP Sammy Wilson warned: “If the Government decides in the face of EU belligerence to cut and run and leave part of the UK languishing in the stifling embrace of the EU, then that would be totally unacceptable to us and many others in the House of Commons.
“It would have implications not just for Brexit legislation — 50% of which would not have passed without DUP support — but also for the Budget, welfare reform and other domestic legislation.”
The East Antrim MP added that treating Northern Ireland differently from the rest of the UK “is the road to parliamentary defeat for any deal which the Prime Minister brings forward”.
“She will not have DUP support regardless of whether the Government tries to bribe, bully or browbeat us into accepting it. However, if the Government decides to stand up to the outrageous, capricious and extortionate demands from Brussels, she will have our full support and she could rally the country behind her,” he said.
However, Downing Street insisted that defeat on the Budget would not amount to a vote of no confidence in the government under the terms of the legislation which provides for fixed-term, five-year parliaments.
Earlier, DUP leader Arlene Foster insisted her party would not accept customs or regulatory checks on goods travelling in either direction between Northern Ireland and Great Britain after meeting EU chief negotiator Michel Barnier in Brussels.
Mrs Foster, who was in Brussels for meetings with key figures including senior MEP Guy Verhofstadt, said: “This is our second day of encouraging representatives of the EU27 to recognise the damage to Northern Ireland by any exit deal which annexes Northern Ireland away from the United Kingdom.
“Firstly, it is clear from our meetings that any form of border in the Irish Sea will impede access for Northern Ireland to new UK trade deals. That removes one of the key benefits of leaving the EU.
“Secondly, ‘best of both worlds’ is not on offer. The EU wants a one-way turnstile from GB and one-way rules from Brussels. Thirdly, if we have a regulatory border, the problem is not on day one after leaving. The problems arise in the years after we leave. Northern Ireland will have to follow EU rules with no power to influence them, and have limited access to the UK single market.”
She called for a “deal that works for everyone” and respects the 2016 referendum result, adding: “We will not burden future generations with a deal which diminishes Northern Ireland’s position in the UK.”
The development came as former foreign secretary Boris Johnson warned that a “backstop” arrangement for Northern Ireland being negotiated by the government would leave the UK “a permanent EU colony”.
In a series of tweets, Mr Johnson said the deal would keep the UK in the customs union and NI in the single market, and would mean increased checks on goods travelling between the province and the British mainland.
Sinn Fein deputy leader Michelle O’Neill said her party had always said that the confidence-and-supply deal between the Conservatives and DUP “will end in tears”.
“The DUP/Tory pact was never about the interests of our economy, the rights of our citizens or our peace and political process,” she said.
“Our task now is to ensure that Ireland doesn’t become collateral damage in the Tory party civil war or in the divisions that are now emerging between the DUP and Theresa May’s government.”
SDLP Brexit spokesperson Claire Hanna MLA said if the DUP is so opposed to the backstop, then logically they should advocate for regulatory alignment for all of the UK.
She added: “These latest threats seem to be indicating that this is now their preference, but they need to have the maturity to come out and say it, instead of hiding behind fear-mongering on constitutional change.”