When Boris Johnson slipped unnoticed into Parliament just over a week ago for a secret meeting with Rishi Sunak, he came in peace.

The aim on both sides was to end the crippling pyschodrama between the two men, which has dogged the Prime Minister as he battles to haul back Labour’s double-digit opinion poll lead.

Instead, the summit lit the fuse for Friday’s explosive resignation by Mr Johnson, which Tory MPs fear could lead to a rupture in the party as damaging as the long-running Brexit wars.

According to his allies, Mr Johnson left the meeting confident that his resignation honours list would be issued intact.

His mood had also been buoyed by separate assurances from Chief Whip Simon Hart that the report by the Commons privileges committee into Mr Johnson’s actions during Partygate would ‘land in the middle of expectations’ and be survivable.

Fast-forward to last Thursday, when Mr Johnson received an emailed letter from committee chairwoman Harriet Harman, warning him that her findings would be strongly critical – meriting a Commons suspension long enough to trigger a by-election in his Uxbridge constituency. 

Then, 24 hours later, another severe blow: the honours list was released – minus the promised peerage for his close political ally Nadine Dorries.

Mrs Dorries resigned as an MP the next day, forcing a by-election in her Mid Bedfordshire seat, followed hours later by Mr Johnson.

The fury in the Johnson camp is hard to overstate: they claim No 10 breached promises made in the meeting by removing five names from the list, and ‘leant on’ Tory MPs on the privileges committee to make their report as damning as possible.

No 10 sources describe both claims as ‘flat-out lies’ and an attempt by the former PM to ‘burn the house down’.

In the words of one Johnson ally: ‘The Government decided over the past two weeks to kill Boris. But it has completely backfired. Boris has shown throughout his career that every time you try to kill him, he just comes back stronger.

‘He will use every conceivable forum to express his views about the direction of travel of the Sunak administration, calling for a low-tax regime which makes the most of Brexit.’

The tensions between the two Tory big beasts are now as bad as any Westminster watchers can remember – ranking alongside the mutual loathing between Margaret Thatcher and Edward Heath, or the toxic feuding of Tony Blair and Gordon Brown.

Johnson supporters argue that Mr Sunak has failed to handle the ‘Boris problem’, acting in a petty manner out of jealousy at his popularity.

They say that the Prime Minister could have halted the Privileges Committee inquiry and bought his loyalty by offering him a post such as the UK envoy to Ukraine.

‘Ordinary Conservative voters will think that it is extraordinary for the Tories to use Harriet Harman of all people to oust a once-wildly popular Tory MP. The PM had multiple chances to stop all this, but instead he risks blowing up the party’.

Sunak supporters say the pettiness is on Johnson’s side, citing the claims by Guto Harri, his former spin doctor, that the ex-PM could not conceal his animosity to his ‘bank manager’ Chancellor and his ‘computer says no’ Treasury.

He said Mr Johnson had recruited Jacob Rees-Mogg to lead the battle against Mr Sunak, giving him ‘carte blanche’ to give the Treasury a ‘massive kick’; Mr Rees-Mogg responded that he was more than happy to ‘tread on some little toes’.

The Johnson camp argues that Mr Sunak wanted the former PM to be ‘eliminated’ to avert the risk of a political comeback, which he has conspicuously failed to rule out.

The first ‘act of aggression’, they say, was the decision three weeks ago by the Cabinet Office to refer Mr Johnson to police over official diary entries which suggested further potential rule breaches by him during the Covid pandemic. 

The same information was also then passed to Ms Harman’s committee; No 10 says the Cabinet Office was simply following the Civil Service code by passing on the new material,

Mr Johnson was en route to deliver a speech in Cairo when he received the letter from Ms Harman making clear that her report was going to be sufficiently critical to merit more than ten days’ suspension from the Commons – enough to trigger a recall process.

A furious Mr Johnson told aides that it ‘confirms our worst fears that this was always intended to be a political hit-job’, and was particularly enraged by lines in the report which said he had deliberately misled Parliament and then compounded the ‘contempt’ by defending himself in evidence to the committee.

No 10 flatly denies the Johnson camp’s version of the two men’s summit.

A source said: ‘When Boris kept asking for reassurances about his honours list being cleared, Rishi explicitly said he couldn’t make any promises and urged Boris to not leave the room thinking that he had. 

‘Rishi’s only role was to pass the list to the House of Lords Appointments Commission (HOLAC) and then receive it back. It was HOLAC which removed the names. A Prime Minister cannot interfere in that process.’

The Johnson allies single out Mr Sunak’s Political Secretary James Forsyth, who has known the PM since they were schoolboys together at Winchester College, by claiming he had removed the names as part of a ‘plot’ against Johnson. The claims are denied by those close to Mr Forsyth, who was the only other attendee at the ‘peace summit’.

One Johnson ally said: ‘No 10 have lied twice. Once when they initially denied that the meeting had even taken place, then when they said Sunak had no involvement or input into the list. But his aides knocked off five without telling us, and contrary to our agreement’.

But a source close to Mr Sunak said: ‘When the Prime Minister met with the former Prime Minister recently, the former Prime Minister raised the matter of peerages with him, to which the current Prime Minister made clear he would follow precedent and not interfere with the process. Any suggestions of promises made or guarantees given are categorically untrue.’

The No 10 sources also scoff at the claims about ‘leaning on’ the committee, insisting it was an ‘obviously independent’ body.

One source said: ‘The reason why the committee hardened its line recently is because of the new information it received about the diary entries, which contain indisputable evidence of rule-breaking. 

‘It was not in our interests for this to happen – it would have been easier for us if Mr Johnson had been let off with a slap on the wrist’.

Though his resignation caught most of Westminster by surprise, Tory party managers had been putting in place contingency plans for a by-election in Uxbridge since the new evidence was passed to the police.

A source said: ‘The red lights started flashing at the end of May, either for Boris to be forced into a by-election or, as has happened, he jumped before he was pushed. 

‘We were also prepared for solidarity resignations, which is why we are already well advanced in Nadine Dorries’ seat.’

Now the battle turns to the Conservative associations: Johnson allies say Tory HQ has been flooded with supportive emails since his resignation. 

Even though party chiefs are technically empowered to block Mr Johnson from standing in a future election, his camp argues that they would be forced into a U-turn by the strength of grassroots feeling.

‘It’s not game over for Boris – it is game on,’ says one. ‘It’s now all-out war.’