Boris Johnson yet again finds himself fighting for his political future as the furore surrounding Partygate refuses to die down, even after the publication of the Sue Gray report, with many of the prime minister’s own MPs continuing to call for his resignation.

       Ms Gray, a respected veteran Whitehall civil servant, last week finally delivered her long-awaited dossier into the string of lockdown-breaking social events that occurred behind the scenes in Westminster while the rest of the country was pulling together, making personal sacrifices and observing strict rules to fend off Covid-19.

       Her inquiry into the multiple newspaper revelations about wine suitcases, “BYOB” garden parties and Christmas quizzes had been delayed by the Metropolitan Police launching an investigation of its own based on the evidence she had collected, which ultimately led to 83 individuals receiving 126 fixed-penalty notices, the PM, his wife Carrie Johnson and chancellor Rishi Sunak among their number and forced to fork over ￡50 each.

       Following the eventual conclusion of the Met’s investigation, Ms Gray was at last able to publish her dossier in full on 25 May, which carried previously unseen photographs and further lurid details of security staff being insulted by drunken revellers, janitors left to sponge claret stains and vomit from the walls of the corridors of power and staff stumbling out of “work events” in the early hours of the morning surreptitiously via a rear door.

       “There were failures of leadership and judgement by different parts of No 10 and the Cabinet Office at different times,” she wrote.

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       “Some of the events should not have been allowed to take place. Other events should not have been allowed to develop as they did.”

       Mr Johnson has repeatedly attempted to ride out the storm of indignation, protesting his innocence with credulity-straining excuses and brazenly rejecting calls to step aside despite being found to have broken his own laws in office.

       While he might have hoped his subsequent apology would draw a line under matters, he must still appear before the Commons Privileges Committee to answer questions about whether he knowingly misled Parliament about Partygate, having regularly denied holding any prior knowledge about what went on.

       Many of his own MPs meanwhile remain incensed and, at the time of writing, 28 have openly called for Mr Johnson’s resignation – including former attorney-general Jeremy Wright – and 16 have admitted to sending letters of no confidence to Sir Graham Brady’s 1922 Committee of axe-wielding backbenchers.

       Under Conservative Party rules, a leadership contest is triggered if 15 per cent of sitting Tory MPs write to its executive committee, whose 18 members meet weekly to discuss party affairs, demanding a change at the top.

       Currently, that would equate to 54 letters from the party’s pool of 369 serving MPs.

       No-confidence letters are handed in confidentially under internal rules, so there is no accurate, publicly available tally of how many have been submitted until the threshold is passed.

       Should the secretive Sir Graham eventually receive enough to proceed, he would be expected to give the PM advanced warning before making a public announcement.

       Mr Johnson would then need to secure 50 per cent of the ensuing secret ballot to survive, equating to around 180 MPs, without which he would be forced to step down, prompting a fresh leadership contest in which the likes of Jeremy Hunt, Liz Truss and Tom Tugendhat are presently being tipped as likely front-runners.

       If he were to secure a majority, the PM’s prize would, in theory, be the guarantee of a full-year’s immunity from further challenges, potentially giving him time to steady the ship, rebuild alliances and strengthen his grip over the parliamentary party.

       In practice, Mr Johnson may find himself unable to survive that period politically: you will recall that, six months after emerging victorious from a confidence vote, Theresa May announced her resignation outside No 10.

       As to how likely these proceedings are to occur this time around, Andrew Bridgen MP, for one, has said he believes the true number of letters in Sir Graham’s hands is “close” to the threshold of 54 but the matter is far from a foregone conclusion and highly unpredictable by nature.

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       Two senior members of Parliament have meanwhile said that a loss in the upcoming by-elections in Tiverton and Honiton in Devon and Wakefield in West Yorkshire could inspire more Conservatives to reach for their feather quills.

       “There will be another round of [no-confidence letters] post the by-elections,” one unnamed MP told The Financial Times.