Theresa May has abandoned her pledge that a deal to keep the UK in the EU customs territory must be “time-limited”, paving the way for likely cabinet resignations.

The prime minister’s spokeswoman refused – four times – to say the “backstop” agreement, to avoid a hard border in Ireland, would have a strict end date, the assurance she set out four months ago.

Instead, No 10 said only that it must be “temporary”, a much looser word that - pro-Brexit ministers fear – will leave the UK locked into an effective customs union for many years to come.

The Independent revealed today that Andrea Leadsom, the Commons leader, is prepared to resign if the compromise is made, with other cabinet ministers believed to be ready to follow her.

Asked if the reworked customs proposals, being negotiated in Brussels, would have “an end date”, Ms May’s spokeswoman said only that it “would be temporary”.

She attempted to head off a backlash by adding: “The prime minister would never agree to a deal which could trap the UK in a backstop permanently.”

However, the U-turn was quickly attacked by Steve Baker, a leading Brexiteer Tory, who said it risked “effectively committing the UK to membership of the single market and customs union”.

“That won’t wash. The British people voted to take back control over money, laws borders and trade,” the former Brexit minister said.

Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Show all 14 1 /14 Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Internal divisions in the Conservative Party have exploded into a bitter public row over Boris Johnson‘s “disgusting” criticism of Theresa May. Some senior Tories furiously denounced the former foreign secretary after he accused the prime minister of having ”wrapped a suicide vest” around Britain Reuters Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Sajid Javid, Home secretary Sajid Javid, the home secretary, rebuked his former cabinet colleague and said: “I think there are much better ways to articulate your differences.” He told the BBC’s Andrew Marr Show that the public wanted politicians to use “measured language” BBC/PA Boris Johnson 'suicide vest' Brexit jibe causes Tory divide But other MPs leapt to Mr Johnson’s defence, as dividing lines ahead of a possible leadership contest begin to take shape. The Uxbridge MP has repeatedly criticised Ms May’s Chequers plan and used a newspaper article on Sunday to suggest it amounted to “wrapping a suicide vest around the British constitution”. His latest salvo at the prime minister prompted immediate condemnation, with one minister publicly vowing to end Mr Johnson’s career over the matter PA Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Alan Duncan, Foreign minister Alan Duncan, a foreign minister who worked in Mr Johnson’s team for two years, wrote on Twitter: “For Boris to say the PM’s view is like that of a suicide bomber is too much. This marks one of the most disgusting moments in modern British politics. “I’m sorry, but this is the political end of Boris Johnson. If it isn’t now, I will make sure it is later.” Getty Boris Johnson 'suicide vest' Brexit jibe causes Tory divide James Brokenshire, Housing secretary Housing secretary James Brokenshire added his voice to the criticism, calling Mr Johnson’s comments ”wrong” He said: “I think he is wrong on this...I think the tone that he has used isn’t right and I think that we just need to be very focused on actually moving forward with the Chequers plan.” AFP/Getty Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Zac Goldsmith But as Tory hostilities spilled over into open public warfare, Richmond Park MP Zac Goldsmith, an ally of Mr Johnson, hit back at Mr Duncan. He wrote: “There are a number of possible motives behind this tweet, but given its author, we can be certain ‘principles’ aren’t one of them.” Getty Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Jacob Rees-Mogg Senior Tory Brexiteer Jacob Rees-Mogg told The Independent he thought Mr Johnson’s “suicide belt” accusation was little more than “a characteristically colourful catchphrase”. He added: “I agree with the sentiment. The criticism of Boris’s wording merely serves to highlight his point. It means more people hear of Boris’s criticism of Chequers and many will agree with him.” Reuters Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Nadine Dorries Nadine Dorries, another Brexit supporter, said Mr Johnson’s opponents were “terrified of his popular appeal”, adding: “Don’t underestimate the vitriol that’ll be directed towards Boris today. He delivered the Leave vote, Remainers and wannabe future PMs hate him.” If Mr Johnson became leader and prime minister he would deliver a “clean and prosperous” Brexit, she said Rex Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Andrew Bridgen Andrew Bridgen said Ms May was to blame for her leadership problems. Asked if Mr Johnson had put a bomb under her leadership, Mr Bridgen said: “I think that Theresa May did that herself when she put forward the Chequers proposals without consulting widely prior to that.” Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Steve Baker, former Brexit minister Steve Baker, the former Brexit minister, warned Ms May the Conservatives faced a "catastrophic split" if she did not jettison her Chequers plan. Mr Baker, who quit the government in July over the scheme, said: “When negotiating, the prime minister needs to demonstrate her intent and also her power to deliver. "If we come out of conference with her hoping to get Chequers through on the back of Labour votes, I think the EU negotiators would probably understand that if that were done, the Tory party would suffer the catastrophic split which thus far we have managed to avoid.” But he insisted he did not want a change in the Conservative leadership, saying Brexiteers did “not want to be in a position of conflict with our own prime minister” Reuters Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Tom Tugendhat The deep divisions on the Tory benches were laid bare as Tom Tugendhat, who chairs the Commons foreign affairs committee and is a possible leadership rival to Mr Johnson, also hit out at the former foreign secretary. Recalling how he encountered a suicide bomber in Afghanistan during his time in the army, Mr Tugendhat told Mr Johnson to “grow up”. He said: “A suicide bomber murdered many in the courtyard of my office in Helmand. The carnage was disgusting, limbs and flesh hanging from trees and bushes. Brave men who stopped him killing me and others died in horrific pain. “Some need to grow up. Comparing the PM to that isn’t happy.” PA Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Alistair Burt Alistair Burt, another Foreign Office minister who worked in Mr Johnson’s team, said: “I’m stunned at the nature of this attack. There is no justification for such an outrageous, inappropriate and hurtful analogy. “If we don’t stop his extraordinary use of language over Brexit, our country might never heal. Again, I say, enough.” AFP/Getty Boris Johnson 'suicide vest' Brexit jibe causes Tory divide It comes amid that Ms May’s former aides drew up a dossier on Mr Johnson’s sexual encounters with the aim of undermining his leadership prospects. The document was compiled in 2016, when the Uxbridge and South Ruislip MP was seen as the main rival to Ms May in her bid to enter No 10. Downing Street and Conservative Campaign Headquaters (CCHQ) both denied having leaked the 4,000 word memo after it was circulated around Westminster AFP/Getty Boris Johnson 'suicide vest' Brexit jibe causes Tory divide Mr Johnson confirmed that his 25-year marriage to wife Marina had ended AP

And Nigel Dodds, the deputy leader of the Democratic Unionist Party, which is propping the Tories up in power, said the U-turn would be “unacceptable”.

“On many occasions both the PM and the Brexit Secretary said the backstop would be time limited. This is critical,” he tweeted.

At a briefing for journalists, the spokeswoman insisted the UK would insist that the backstop “needs to” end no later than December 2021.

However, without a legal requirement for that to happen, in the Brexit withdrawal deal, it would depend on the EU agreeing later that as-yet unproven technology has produced a solution.

If it refused, the Irish backstop would then lock the entire UK permanently into an effective customs union, unable to sign its own trade deals, many Tories fear.

Other cabinet ministers believed to be prepared to resign include Esther McVey, the work and pensions secretary, Penny Mordaunt, the international development secretary and even Liam Fox, the international trade secretary.

There are also doubts over the future of Brexit secretary Dominic Raab, who has repeatedly said publicly that the customs union plan must be time-limited.

Asked if Ms May feared cabinet walkouts, the spokesman said: “The prime minister is focused on getting the best possible deal and that’s what she is working to deliver.”

And she insisted: “Our position is that this future economic relationship needs to be in place by the end of December 2021 at the latest.”

Andrew Bridgen, another Brexiteer Tory, urged fellow MPs to act by sparking a vote of confidence in the prime minister’s leadership.

“They should put the letters in and test the prime minister’s popularity with the party,” he told the BBC.

Mr Bridgen said Tory MPs had been “holding back”, but that the situation would change “if it becomes clear that we are stopping in a customs union”, adding: “It’s coming to a head this week.”