The Democratic Unionist Party (DUP) has threatened to vote down the budget at Westminster later this month if Theresa May agrees a Brexit deal that violates their negotiating red lines.
This would end the agreement the party entered into with the Conservatives after the last election.
The DUP’s latest threat came in a background briefing to broadcasters as British and EU negotiators sought agreement on the backstop to guarantee that there will be no hard border after Brexit.
This is far from #TakeBackControl. In the referendum both sides said Leave meant leaving the customs union & single market. Yet this backstop inevitably means chequers, staying in both, no say in either, and no right to escape. No10 must #ChuckChequers now 4/4
— Boris Johnson (@BorisJohnson) October 10, 2018
"If we are not happy with what happens next week we won't be bounced into anything. If she doesn't take our concerns on board, we will take the view that Theresa May is not the leader to take us through to a safe Brexit," a DUP source told the BBC and Sky News.
Amid reports that Britain is preparing to agree to a backstop that would involve regulatory checks between Great Britain and Northern Ireland and keep the whole of the UK in a temporary customs union, Boris Johnson said it would make Britain "a permanent EU colony".
In a series of tweets, the former foreign secretary said the deal would mean that Britain could not escape EU laws and the jurisdiction of the European Court of Justice until the EU agrees.
"This backstop keeps the UK in the Customs Union, keeps Northern Ireland in the single market, and almost certainly enhances NI/GB checks. It will apply after 2020 unless the EU agrees it won't. And they will only agree if we keep our rules in lockstep with theirs," he said.
In the House of Commons on Wednesday, Mrs May called on MPs from all parties to “put the national interest first” and back the Brexit deal she brings back from Brussels. Asked if the prime minister believed she could rely on DUP votes, a Downing Street source referred to the confidence and supply arrangement.
“The confidence and supply arrangement we have with the DUP is a matter of record,” he said. Under the agreement, which secured an extra £1 billion in spending for Northern Ireland, the DUP committed to support the government on all motions of confidence; and on the Queen’s Speech; the budget; finance Bills; money Bills, supply and appropriation legislation and estimates.
"In line with the parties' shared priorities for negotiating a successful exit from the European Union and protecting the country in the light of recent terrorist attacks, the DUP also agrees to support the government on legislation pertaining to the United Kingdom's exit from the European Union," the agreement states.
The prime minister’s official spokesman declined to comment directly on the DUP’s threat. But he confirmed that the loss of a vote on the budget would not automatically trigger an election.
“The Fixed Term Parliaments Act sets out the circumstances for a confidence vote,” he said.
Under the 2011 legislation, only an explicit vote of no confidence in the government or a motion backed by two-thirds of MPs calling for an election can precipitate one.
