Boris Johnson has triggered a fresh political storm by accusing Theresa May of wrapping a ‘suicide vest’ around Britain – and handing the detonator to Brussels.

The former Foreign Secretary uses a blistering article in today’s The Mail on Sunday to condemn the Prime Minister’s ‘feeble’ handling of the Brexit negotiations, her ‘pathetic’ Chequers deal and the Government’s ‘semi-masochistic’ relationship with the EU.

In his first public comments since his marriage split, Mr Johnson paves the way for a potential leadership bid by demanding Mrs May take a more aggressive stance in the Brexit negotiations.

Boris Johnson, pictured yesterday leaving the Oval, has condemned Theresa May's negotiating strategy with Brussels over Brexit, describing her Chequers deal as wrapping a 'suicide vest' around the British constitution

Mr Johnson is especially critical over Theresa May's Northern Ireland 'backstop' agreement

Amid an increasingly febrile atmosphere at Westminster, this newspaper can also reveal:

The contents of a ‘dirty dossier’ on Mr Johnson, which was drawn up by Mrs May’s advisers as part of an alleged attempt to ‘smear’ him;

Leaked details of the ‘chuck Chequers’ manifesto drawn up by arch-Brexiteers, which calls for billions to be ploughed into income tax cuts, the NHS and the Armed Forces;

That the Foreign Secretary, Jeremy Hunt, is calling on the Prime Minister’s political enemies to give her ‘the flexibility and room’ to strike a good deal for Britain. Writing in The Mail on Sunday he says she will fulfil ‘the will of the people’.

Mr Johnson’s colourful private life was thrust on to centre stage on Friday when it was announced he was separating from his barrister wife Marina Wheeler amid claims of an affair with a blonde Conservative aide.

Though the woman has not yet been named, Carrie Symonds, the party’s former director of communications, was last night linked to the former Foreign Secretary.

Some observers have speculated Mr Johnson’s marital crisis could torpedo his lifelong dream of becoming Prime Minister, but in today’s article he makes clear his ambitions are undimmed as he ferociously attacks Mrs May’s plan to keep the UK tied to many EU rules.

‘We have opened ourselves to perpetual political blackmail,’ he writes. ‘We have wrapped a suicide vest around the British constitution – and handed the detonator to [EU Brexit negotiator] Michel Barnier.’

Mr Johnson, right, and his wife Marina announced they are to divorce after the former Foreign Secretary was linked to former Tory Party spin doctor Carrie Symonds, left

Mr Johnson complains that instead of striking a ‘giant and generous free trade deal’, Mrs May says ‘yes sir, no sir, three bags full sir’ to the EU.

He writes: ‘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 £39 billion, 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 directs his attack on Mrs May’s promise to Brussels that, if a solution to the Irish border problem cannot be found, then Northern Ireland would remain in the customs union and the Single Market: ‘in other words, part of the EU. And that would mean a border down the Irish sea’

Mr Johnson claimed the Chequers deal was like wrapping a suicide vest around the British constitution

Describing the so-called ‘backstop’ as ‘insanity’, Mr Johnson says of Mr 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.

‘In a weird semi-masochistic way we have created the means by which the EU can bully us. We have conspired in this threat to the Union. We have put our own heads deliberately on the block.’

Meanwhile, in a separate Mail on Sunday article, Mr Hunt calls on the Prime Minister’s critics to unite behind her, saying: ‘She is better than anyone I know at holding the line in the face of intense pressure’, adding that she ‘would never recommend a deal that was inconsistent with what the country voted for’.

Mr Hunt – who backed Remain in the referendum and once floated the idea of a second poll on the final deal – now says he is determined to push on with Brexit. ‘More people voted to leave the EU than have ever voted for any political party in our country’s history,’ he writes. ‘Nothing would be more damaging for our democracy than for the political establishment to try to unpick that decision’.

Mr Hunt and Mr Johnson’s clash comes amid intensifying speculation about an imminent leadership challenge to Mrs May.

In an apparent attempt to undermine Mr Johnson’s expected bid for power, a secret file detailing his affairs and political controversies was circulating in Whitehall last week. It was compiled by members of Mrs May’s team during the 2016 Election, but Tory HQ stressed yesterday that it was not connected to its distribution.

Meanwhile, the ‘chuck Chequers’ proposal – described as an effective manifesto for a Johnson leadership – had been due out in the coming days, but was spiked at the last minute. The document, drawn up Jacob Rees-Mogg’s European Research Group, was pulled following rows over some of the policies.

A draft of the blueprint seen by this newspaper shows that the MPs were planning to give voters a ‘Brexit bonus’ by cutting income tax, business rates, capital gains tax, stamp duty and VAT on female hygiene products, home insulation and domestic fuel.

Billions would also be spent on schools, the NHS and defence – including a ‘nuclear missile shield’.