PM tries to rally support after Arlene Foster’s party warns it may vote down budget over Irish backstop plan

Theresa May is fighting to keep the delicate Brexit negotiations on track after the DUP threatened to vote down the budget and bring down her premiership if a divorce deal meant that Northern Ireland was treated separately from the rest of the UK.

The prime minister responded by summoning senior cabinet members to Downing Street on Thursday, where she was expected to update them on progress amid signs that the sabre-rattling DUP and the Tory right were acting in concert against her.

Ministers are expecting to hear more about the status of the withdrawal agreement – which includes the Irish border backstop – although its text is deemed so sensitive that it is not expected to emerge until European leaders meet next week.

Pro-remain Tory MPs will form group to vote down May's Brexit deal Read more

Senior DUP sources had warned that their 10 MPs would vote against the budget at the end of this month, potentially leaving May without a majority, if she gave away too much at next week’s crunch summit in Brussels, abruptly ending the confidence and supply agreement that has kept May in Downing Street.

A few hours later, DUP leader Arlene Foster, in Brussels for talks with EU officials, said that she had “been telling people about our red line” and added: “We can’t have a customs or regulatory barrier in the Irish Sea because that would cause us to be a rule-taker from Europe.”

The DUP threat comes days after the hard-Brexit ERG indicated that its MPs – thought realistically to amount to around 40 – would also be prepared to vote against the budget a few days after it is delivered by Philip Hammond on October 29.

Downing Street insisted that a defeat on the budget would not amount itself to a vote of no confidence under the terms of the fixed term parliament act, but in reality failing to pass a finance bill would amount to a humiliation for Theresa May, and put her position as prime minister in jeopardy.

Boris Johnson added to the pressure on May, saying that he feared that in order to placate the DUP, May would negotiate a different customs backstop that “makes the UK a permanent EU colony” because it would keep the whole of the UK inside the EU’s customs union if a free trade deal could not be agreed by December 2020, the end of the transition period.

“We cannot escape EU laws and [the] ECJ until they allow us to – which they may never do. That’s not what the biggest majority in our history voted for,” the former foreign secretary tweeted.

Boris Johnson (@BorisJohnson) This is an important moment. Clearly No10 are negotiating a “backstop” that makes the UK a permanent EU colony. We cannot escape EU laws & ECJ until they allow us to – which they may never do. That’s not what the biggest majority in our history voted for #NoColonyStatus 1/4

Last night, DUP MPs fired a warning shot by abstaining on a Labour amendment to the agriculture bill. The unionist party normally votes with the Conservatives in the Commons, although the amendment was nevertheless defeated.

Last December the UK and EU agreed there would be regulatory alignment between Northern Ireland and the Republic of Ireland in the event of no deal, the so-called backstop. At the same time both sides agreed there would be no barrier in the Irish Sea after the DUP objected. These contradictory aims sowed the seeds for the current impasse.

Cabinet ministers expected to attend the Downing Street briefing include foreign secretary Jeremy Hunt and home secretary Sajid Javid, both of whom are considered key figures in cabinet, as well as cabinet office minister David Lidington and Michael Gove and Gavin Williamson.

The expectation is that they, and other senior members, would be given an informal insight into the negotiations ahead of a critical meeting of the full cabinet on Tuesday morning, which will have to sign off May’s position ahead of the European summit on the Wednesday and Thursday.

Those attending are thought to all be members of the EU Strategy and Negotiations committee – previously dubbed the Brexit “war cabinet” – which has not formally met since before the Chequers summit. But Downing Street insiders insisted that it was not a formal meeting, and so not a decision-making body.

The embattled May did win some support from former home secretary Amber Rudd, who wrote to all Tory MPs urging them to fall in line behind the prime minister. “The PM is in the final stages of negotiating a deal. Alternative proposals at the last hour are neither viable nor preferable,” she said.

The ex-minister was hitting back at former Brexit secretary David Davis, who had warned on Tuesday that if May remained on her current course, by signing up to a “common rulebook” for food and goods after leaving the EU, it would have “dire consequences” at the ballot box.

Rudd told her colleagues: “The electoral consequences of our decision are not the first thing the government is thinking about anyway, but the politics are pretty much the same as the economics. They dictate a willingness to compromise and an adherence to realism and common sense.”

May, meanwhile, publicly signalled for the first time that she was hoping to win the support of Labour MPs to endorse her Brexit deal when it is subject to a meaningful vote at around the end of November, if the negotiations successfully conclude.

The prime minister was asked by Ken Clarke, the veteran pro-EU former chancellor, to ignore hardline Brexiters and bring forward a deal acceptable to centrists MPs on both sides of the Commons, which he said would reveal that “hardline Eurosceptic views” of the “Bennites” in the Labour leadership and the “rightwing nationalists” on the Tory benches were in a minority.

In response, May said: “I would hope that everybody across this whole House will put the national interest first” in a clear pitch for the votes of Labour MPs. It had been reported that as many as 30 Labour MPs might be prepared to vote with May if the alternative was a “no-deal” Brexit.

Labour insiders insisted that the 30 figure of potential rebels was too high and only a small number of the party’s MPs, many of whom had already voted with the government, would be likely to side with the Tories.

Simon Coveney, Ireland’s foreign secretary and deputy prime minister, told reporters in Dublin that the EU understood that May must get a deal that was “sellable” in Westminster and that it would be unhelpful to publish a backstop while sensitive negotiations were ongoing.