Boris Johnson deliberately misled parliament over Partygate and was part of a campaign to abuse and intimidate MPs investigating him, a long-awaited report by the privileges committee has found. In an unprecedented move, the cross-party group said he “closed his mind to the truth” and would have faced a 90-day suspension from the Commons had he not quit in rage at its conclusions last week. Johnson was also found to have knowingly misled the committee itself, breached Commons rules by partially leaking its findings last Friday, and undermined the democratic processes of parliament. As a result, it was recommended Johnson be banned from getting the pass granted to ex-MPs that allows them privileged access to the Westminster estate. Johnson was originally set to face a suspension from parliament of 20 days – enough to trigger a recall petition that would have probably led to a byelection. But the committee said his blistering attempts to intimidate it last Friday would have increased the punishment to 90 days. Two MPs on the committee – one Labour and the other from the SNP – had pushed for Johnson to be expelled from parliament. But the final report and punishment was signed off unanimously by all seven members. “He deliberately misled the house … on an issue of the greatest importance to the house and to the public, and did so repeatedly,” the report said. It added his attempt to brand the committee a kangaroo court “amounts to an attack on our democratic institutions”. Johnson’s argument that he believed all the parties in Downing Street were legal was filleted by the committee. “That belief … has no reasonable basis in the rules or on the facts,” it said. “A reasonable person looking at the events and the rules would not have the belief that Johnson has professed.” The findings came in an excoriating 106-page report published on Thursday, which also confirmed that the government last month handed over evidence of a further 16 gatherings at No 10 and Chequers that were “potentially problematic”. Johnson insisted all those events were within the rules and necessary to provide support to his pregnant wife, Carrie. The committee said if it emerged his assurances were untrue, “he may have committed a further contempt” of parliament. Across the televised hearing and in written evidence, Johnson was accused of seeking to “re-write the meaning of the rules and guidance to fit his own evidence”. The committee criticised “the frequency with which he closed his mind” to the facts and “what was obvious”, leading it to concludethat the former prime minister “was deliberately closing his mind”. So forensic was the committee’s inquiry, that its MPs went into No 10 to measure a room where Johnson was pictured holding a drink with others stood around him not socially distanced. It said his claim that it had been necessary to boost staff morale by attending the event after the departure of two senior No 10 aides did not provide licence for his “conveniently flexible interpretation of the rules on gatherings”. As a result of the angry response from Johnson and his allies, it was reported that the MPs on the committee had been offered increased security. The committee said Johnson had attacked “in very strong, indeed vitriolic, terms the integrity, honesty and honour of its members”. Johnson accused the committee, which has a Tory majority and a Labour chair, of trying to “bring about what is intended to be the final knife-thrust in a protracted political assassination”. He said their findings were “preposterous” and a sign of “desperation”. “This report is a charade,” Johnson said in a 1,700-word rebuttal. “I was wrong to believe in the committee or its good faith. The terrible truth is that it is not I who has twisted the truth to suit my purposes. It is [the chair] Harriet Harman and her committee.” Rishi Sunak dodged questions about the report, in a short interview on Thursday morning in the hours before its publication. He denied he was “frustrated” by Johnson’s interventions over the past week, but refused to say whether the former prime minister should be allowed to stand again as a Tory MP. Sunak added: “These are matters for the House of Commons, and parliament will deal with it in the way that it does.” The moment is potentially one of major jeopardy for Sunak, given the fragile peace he sought to build in the Conservative party has fractured further in recent days. The row about the report has already resulted in Johnson sparking a difficult byelection next month by standing down and mounting furious attacks against one of the Tory committee members. Tory MPs will have to decide how to vote on the report’s findings next Monday. Many are likely to endorse the result of the more than year-long inquiry, but there could be a damaging split on the government benches if Johnson’s allies refuse to do so.