Boris Johnson has made an 11th-hour intervention that looks set to delay the publication of a report expected to find he misled parliament over Partygate until Thursday at the earliest. Having quit as an MP in fury on Friday after receiving a private copy of the findings, lawyers for the former prime minister sent a letter at 11.57pm on Monday night that is being considered by the privileges committee. MPs on the cross-party group, which has a Tory majority and Labour chair, had been hoping to bring their year-long inquiry to an end on Wednesday with a definitive conclusion about Johnson’s conduct. But the letter from Johnson, as well as a large operation to draft the report and attach reams of evidence significantly earlier than planned to ensure it is “watertight”, has slowed down proceedings. No information was given by the privileges committee about the arguments made by Johnson’s legal representatives, but a spokesperson said it is “dealing with these and will report promptly”. Downing Street wants the report published as quickly as possible, so that the Commons leader, Penny Mordaunt, can announce at her weekly business statement on Thursday morning when the vote on its findings will be. Harriet Harman, the committee’s chair, has privately made direct appeals to the government for a vote on the report and that is the clear expectation of its six other members, the Guardian has been told. However, a senior government source said there was a “live discussion” about how to avoid the vote causing further embarrassment for the Conservative party, given relations between Johnson and Rishi Sunak have significantly deteriorated. The motion could be worded to “note” the privileges committee’s report rather than accept it – a seemingly small but significant difference that may avoid Johnson allies voting against it to protect him, the source said. Any attempt by the government to avoid explicitly accepting the privileges committee’s report could spark the ire of opposition parties and lead them to table amendments. A decision about when to schedule the vote has not been made yet, but sources suggested next Monday was the most likely date. No 10 and the whips’ office were contacted for comment, but neither would confirm anything regarding the timing or wording of the motion until the privileges committee’s report had been published. The vote will be potentially thorny for the government. Conservative whips estimate that about two dozen of Johnson’s supporters are prepared to vote against the privileges committee’s report. Even those who were formally ardent supporters of the former prime minister signalled they were likely to endorse the report – or at least abstain instead of voting against. “He can’t just keep burning the house down,” said one. Another added: “It looks so petty. The sooner he takes it on the chin and backs off, the more of a positive legacy he’ll leave behind.” Johnson has denied any wrongdoing. He said: “The privileges committee should publish their report and let the world judge their nonsense. They have no excuse for delay.” He added: “Their absurdly unfair rules do not even allow any criticism of their findings. I have made my views clear to the committee in writing – and will do so more widely when they finally publish.” Given he formally quit the Commons on Monday, the privileges committee will be unable to enforce its expected verdict of a more than 10 day suspension from the Commons. Such a move would probably have triggered a recall petition, leading to a byelection anyway. In his resignation letter, Johnson defended his statements in parliament denying Covid rules had been broken. “[The privileges committee] know perfectly well that when I spoke in the Commons I was saying what I believed sincerely to be true and what I had been briefed to say, like any other minister.” But the committee is expected to find in its report that Johnson was not given assurances the events in question were within the rules.