Boris Johnson has called for a Conservative MP on the privileges committee to resign as a furious blue-on-blue row erupted on the eve of a long-awaited report that will find he misled parliament over Partygate. In an attempt to disparage the findings of the report, Johnson called allegations that Bernard Jenkin attended a birthday drinks in parliament during Covid restrictions a “total contempt of parliament” and said he has “no choice” but to recuse himself from the panel. The move was called “utterly desperate” by senior Tories who believe the storm was blown up by Johnson to undermine the privileges committee’s damning findings against him, which are set to be published on Thursday. But Johnson’s allies lined up to pile pressure on Jenkin, who is one of four Tories on the committee that signed off its report into Johnson’s Partygate denials after a year-long inquiry. Jenkin, parliament’s most senior select committee chair and a former Tory deputy chair, was said by the Guido Fawkes website to have attended an event on 8 December 2020 in parliament. It was reportedly the date of his wife’s birthday, with a “drinks party” held by Eleanor Laing, a Commons deputy speaker, in her office. Several people were in attendance, including Jenkin, it was claimed. Guido Fawkes said when it contacted Jenkin for comment that he insisted: “I did not attend any drinks parties during lockdown.” When pressed further to see if he would deny having a drink at his wife’s birthday celebration, Jenkin said: “I don’t recall.” Laing told Guido Fawkes the event was in the rules. In a statement, she said: “At the beginning of the pandemic I took advice on how many could be present in a room, I had the room measured and I kept a two metre ruler so that I could always verify that nobody who was working here was put at risk.” Bernard Jenkin, his wife and a spokesperson for the privileges committee were all contacted with a request for comment from the Guardian. An ally of Jenkin said it was a work event held by senior figures in the Women2Win network, which encourages more Tory women to stand for political office, and that he arrived to collect his wife. At the time of the event, the second national lockdown had recently lifted across England and the “tiers” system was in force. London was in tier 2, meaning households were not allowed to mix indoors apart from support bubbles, while the “rule of six” applied outdoors. Everyone who could work from home was told to do so, but key workers – which included politicians – were still permitted to travel into the office and gather indoors for work purposes, so long as social distancing was observed. Some Tory MPs reacted with fury, believing Johnson had engineered the new claims emerging about Jenkin to derail the privileges committee investigation. One said: “Boris will desperately be opening his little black book and desperately trying to cast aspersions elsewhere. He would burn parliament to the ground around him.” Another added: “We’re not far off him asking Andrew Bridgen for his tinfoil hat supplier.” Nadine Dorries, the former culture secretary, is understood to have written to the clerk of the privileges committee about the alleged event, calling for its chair, Harriet Harman, to look into the claims. Another Johnson ally and ex-cabinet minister said: “I am absolutely appalled by this behaviour taking place on the parliamentary estate. Clearly, Jenkin should be appearing before his own committee; there should be a full investigation.” Any rule-breaking is unlikely to be investigated by the privileges committee. Its remit is specifically to look at contempt of parliament allegations. Since last April, it has been investigating whether Johnson misled the Commons by repeatedly claiming all Covid rules were complied with during lockdown, and that he had been assured any events in No 10 were within the rules. Jenkin was one of the seven MPs who grilled Johnson about his rule-breaking during a televised evidence session in March. He asked the former prime minister: “A leaving do for everyone else around the country was not acceptable under the guidelines or the rules, so why was it acceptable and necessary for work purposes in No 10?” The Liberal Democrats sought to keep the focus on Johnson. Its deputy leader, Daisy Cooper, said: “This a typical distraction tactic from Boris Johnson that doesn’t change the fact he broke the law and lied about it. “The Conservative party is now in a full blown civil war, while people struggle to afford to pay their mortgage or get a GP appointment. This whole unedifying spectacle needs to be brought to an end as soon as possible.” The privileges committee had hoped to sign off its report into Johnson’s conduct on Monday, but an 11th-hour submission at 11.57pm from him delayed proceedings. The committee met multiple times on Tuesday and signed off its report that evening. The 30,000-word findings are expected to be published on Thursday morning. The government is set to announce that same day when a vote will be held formally on its findings – though Monday is the most likely point, given Downing Street hopes to bring the issue to a speedy close.