The Northern Irish DUP has said it will not support the government if it tables a fresh meaningful Brexit vote because “the necessary changes we seek to the backstop have not been secured”.
The move comes after Theresa May announced she would step down as Prime Minister sooner than expected to help get her plan through.
Crucially, the party will vote against the deal, rather than abstain, which could be the fatal blow.
The DUP’s hold-out will raise questions about when May will stand down if her deal fails, and has led to fresh speculation over how to end the deadlock.
Asked about the pressure on the DUP to back the deal, party leader Arlene Foster told Sky News: “I don’t think it’s a case of rescuing Brexit because we very much want to see Brexit happening, we believe in Brexit, we believe in the opportunities that are there post-Brexit.
“We wish we were able to spend more time talking about the global opportunities that we believe are there for the nation post-Brexit.
“But instead we have become bogged down in a process, but that process has a Withdrawal Agreement with a backstop that will cause damage to the UK, and for us that is the critical point.”
Pinning the blame on May, she said: “Now we are in a situation where we cannot sign up to the Withdrawal Agreement and it’s all because the Prime Minister decided to go for that backstop way back in December 2017.”
The DUP leader said that although Brexit was “incredibly important” to her, “it’s not the most important issue”.
“The most important issue for me, for the Democratic Unionist Party, for our 10 MPs, is the preservation of the union,” she said.
DUP deputy leader Nigel Dodds, replying to a journalist asking if they might abstain on May’s deal, said: “The DUP do not abstain on the Union.”
The backstop would keep Northern Ireland aligned with the rest of the EU on trade regulations to prevent the imposition of a hard border with the Republic of Ireland.
Any divergence in the rules between Northern Ireland and the rest of the UK could lead to internal boundaries equivalent to a border in the Irish Sea, backstop critics fear.
The backstop is a major plank of the Irish Government’s strategy and would only be implemented if a better solution was not found during transition negotiations on long-term arrangements after an orderly Brexit.