Boris Johnson in ‘suicide vest’ jibe at Theresa May on Brexit

Johnson launched the attack amid further focus on his private life following the announcement that he has separated from his wife Marina Wheeler and the couple are divorcing.

The Hard Brexiteer’s latest assault on May’s handling of negotiations with Brussels will fuel speculation about his own leadership ambitions.

Johnson quit the Cabinet in opposition to May’s Chequers plan which would see the UK remain closely aligned with EU rules on goods.

Writing in the Mail On Sunday, he said: “At every stage in the talks so far, Brussels gets what Brussels wants.

“We have agreed to the EU’s timetable; we have agreed to hand over £39bn, for nothing in return.

“Under the Chequers proposal we are set to agree to accept their rules – forever – with no say on the making of those rules.

“It is a humiliation. We look like a seven-stone weakling being comically bent out of shape by a 500lb gorilla.”

He also lashed out at the Northern Ireland “backstop” – the measure aimed at making sure there is no hard border with Ireland.

Under the EU’s version of the plan, if no trade deal with the UK resolved the issue, Northern Ireland would effectively remain part of the single market.

Johnson said: “We have opened ourselves to perpetual political blackmail. We have wrapped a suicide vest around the British constitution – and handed the detonator to Michel Barnier.

“We have given him a jemmy with which Brussels can choose – at any time – to crack apart the union between Great Britain and Northern Ireland.”

The UK’s alternative backstop and the Chequers plan would both mean “agreeing to take EU rules, with no say on those rules”, leaving the country a “vassal state”.

He said: “We have managed to reduce the great British Brexit to two appalling options: either we must divide the Union, or the whole country must accept EU law forever.”

Johnson said there were “far better technical solutions” to the Irish border issue.

The former Cabinet minister’s comments drew a furious response from Tory MP and ex-army officer Tom Tugendhat – who has been viewed as a possible rival in a leadership contest.

“A suicide bomber murdered many in the courtyard of my office in Helmand,” he said. “Comparing the PM to that isn’t funny.”

While Foreign Office minister Sir Alan Duncan said: “For Boris to say that 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.”

But in a further indication of the toxic nature of relations within the Tory party, Brexit-backer Zac Goldsmith responded to Sir Alan by saying: “There are a number of possible motives behind this tweet, but given its author, we can be certain ‘principles’ aren’t one of them.”

Johnson’s own leadership ambitions may have suffered a blow by the revelation that his marriage has broken down, although some Westminster commentators suggest having the break-up made public now clears away a potential obstacle on the way to Number 10.

In a sign of the febrile atmosphere within the Conservative Party, the Sunday Times reported that Mrs May’s aides had drawn up a dossier on Mr Johnson at the time the 2016 leadership contest.

It was not used after his campaign failed to get off the launch pad, but the newspaper reported the 4,000-word “war book” was circulating in Westminster last week amid claims “black ops” attacks were being planned against the prominent critic of the Chequers plan.

Officials at Downing Street and Conservative Campaign Headquarters (CCHQ) denied circulating the document.

With tomorrow marking just 200 days until the UK’s exit from the EU, Johnson’s successor as Foreign Secretary Jeremy Hunt pleaded for Tories to get behind Mrs May and the Chequers plan.

Ahead of a potentially difficult Conservative Party conference, Hunt said the Prime Minister’s efforts to achieve the best outcome for Britain “will be greatly strengthened if we are united behind her”.

In a Mail On Sunday article, he said: “We should not rush to judgment on a deal that is still under negotiation.

“Nor should we assume that unacceptable further concessions will ‘inevitably’ be made on the Chequers proposals. I know this Prime Minister and she would never recommend a deal inconsistent with what the country voted for.”

In a pointed remark apparently aimed at Brexiteers, he added: “Nobody else has a detailed plan that both delivers on the instruction of the British people and has a chance of succeeding in the negotiations.”