PM under pressure as leading Brexiters and Tory remainers come out against proposals

Theresa May’s Brexit plan is under siege from across the Tory party as she attempts to overcome the final sticking points with Brussels in time to push it through a critical meeting of her cabinet ministers on Tuesday.

As time runs out, leading Brexiters have told the prime minister they remain deeply opposed to her version of an exit mechanism that would prevent the UK unilaterally quitting a temporary customs arrangement if Brexit talks collapse.

Andrea Leadsom, the Commons leader and a prominent Eurosceptic, said she was “sticking in government” to make sure the UK did not end up trapped in a customs arrangement, warning May she would struggle to get her plans past MPs.

May also faces a growing rebellion from the remainer wing of her party with rumours that four more pro-Europe ministers are on the brink of resigning after the departure of the transport minister Jo Johnson last week.

One former cabinet minister told the Guardian it was a question of “when and how many go, rather than if”, while other prominent Tory remainers claimed they were aware of a several ministers “who are hanging on by their fingertips”.

As the prime minister struggled to keep her Brexit plans – and her party – on track, her chief Brexit adviser, Olly Robbins, was in Brussels on Sunday trying to thrash out the final details of the withdrawal agreement before Tuesday.

EU diplomats have cautioned against over-optimism about a breakthrough this week, with the legal text said to remain “fluid”. Sources suggested negotiators on both sides had agreed it would be impossible for the UK to unilaterally exit its backstop on Northern Ireland, a key Brexiter demand.

But as some sought to reconcile the Tory party’s divided positions, Boris Johnson, the former foreign secretary, used his Telegraph column published in Monday’s newspaper to call for a Cabinet mutiny and wrote that the government ‘‘seemed to be on the verge of total surrender”.

The prime minister, he continued, had “recommended to the cabinet not only that we agree to stay in the customs union under the so-called ‘backstop’ arrangement, but that we actually abdicate the power to leave that backstop.

“Under the shameful proposals now before cabinet it will be up to some joint UK/EU committee, or some ‘independent arbitration mechanism’ to decide whether the UK – an ancient and sovereign nation – is finally allowed to come out.”

A review mechanism involving a joint committee, with European court of justice oversight, allowing May the ability to claim that her all-UK customs union backstop was not permanent, is likely to be the best the government can expect in negotiations.

The talks are now focusing on EU demands on “level playing field” commitments over competition and state aid, as well as social and environmental protections, to ensure UK businesses are not able to undercut European industry.

The UK has already said it is open to non-regression clauses in a future trade deal that would prevent it from lowering standards. Brussels is demanding “dynamic” alignment, which would force parliament to “cut and paste” EU regulations as they come in after Brexit, without giving Britain any say.

The Guardian has learned that EU member states are insisting on having time to scrutinise this part before it is made public. One senior diplomat said: “We cannot be left in the dark on this now, it is too important.”

UK government sources attempted to play down expectations that negotiators would reach agreement in time for the cabinet meeting. If they fail, there will not be an emergency EU summit in November and the prime minister will have to press ahead with “no deal” preparations in case negotiations ultimately falter.

May is expected to face anger from cabinet Brexiters over her exit mechanism plans.

Yet cabinet sources suggested that disgruntled ministers would stop short of quitting over the exit mechanism plan. Even if they were “bounced” into agreeing to the deal, May would still face a serious challenge getting it through the Commons.

Leadsom told BBC Radio 5 Live: “I am working towards getting a deal that does not require the UK to be stuck, trapped in a customs arrangement. I’m sticking in government to make sure that’s where we get to in the end.”

She added: “The UK cannot be held against its will in a customs arrangement. It must be capable for the United Kingdom to decide to leave that customs arrangement and it cannot be something that the European Union can then hold us to.

“And, frankly, it’s because that would be to then fail to fulfil on the will of the people expressed in the referendum and I very much doubt that we would get it through parliament.”

Cabinet Brexiters have pushed for a unilateral route, with the international trade secretary, Liam Fox, the first to say publicly the power to leave the backstop – the UK’s insurance policy if talks fail – should rest with the “sovereign” British government.

The education secretary, Damian Hinds, said the EU would not accept that plan. “If you have too hard a line about saying, ‘well, we must just have a totally unilateral exit, or there’s an absolutely fixed, hard end date’, that is very, very unlikely that is going to be negotiable with the other side,” he said.

He urged an alliance of Conservative hard Brexiters and the DUP, who have said they will join forces to vote down May’s withdrawal plans, to “think about the alternatives”, saying there would be “trade-offs” in any deal.

The latest plan under discussion is believed to include the option of pushing ahead with a “successor agreement” that would set out the full trading relationship between the EU and UK by late 2020, and extending the transition period if needed.

As a last resort a UK-wide backstop would kick in, with Northern Ireland aligned more closely with single market rules to avoid a hard border, inevitably prompting a showdown with the DUP, who oppose any trade border in the Irish Sea.

The prime minister also faces growing pressure to press the button on her no-deal preparations. Gen Sir Nick Carter, chief of the defence staff, told the BBC the military “stands ready to help in any way we can” in the event of no deal.