A privileges committee report that could criticise Conservative MPs who attacked an inquiry into Boris Johnson may be released as early as next week, potentially plunging Rishi Sunak into renewed party infighting. While Johnson allies say the former prime minister is keen to assist in a period of “peace and quiet” after Monday’s Commons vote, which endorsed the privileges committee’s findings that he had lied repeatedly to parliament, the additional report could jeopardise that. In the 106-page investigation that found Johnson misled MPs in repeatedly assuring the Commons he was unaware of lockdown-breaching parties, the Conservative-majority committee condemned what it called “a sustained attempt, seemingly coordinated” to undermine its members and the inquiry process. It said it would produce a supplementary “special report” into this, which could be published next week. While it is not known what the extra report will say, even if it does not name MPs it could anger Johnson’s supporters, jeopardising Sunak’s attempts to placate them. Some of Johnson’s Tory allies have argued that whether or not they agree with the decision about misleading parliament, the committee’s decision to suspend him for 90 days – not enforceable as he has stepped down – and the special report show overreach. Downing Street has steadfastly refused to give Sunak’s opinion on Monday’s vote, or even whether he believed Johnson did mislead MPs, after the prime minister was absent from the entire debate. While the deliberate ambiguity avoids the risk of further upsetting Johnson-loyal Conservative MPs, it prompted Labour and the Liberal Democrats to label Sunak as terrified of his own party and is likely to be exploited by Keir Starmer at Wednesday’s prime minister’s questions. A series of ministers were among the 354 MPs who approved the report on Monday, 118 of them Conservatives. Seven MPs voted against. Asked whether Sunak had a view on the decision, his spokesperson said: “The prime minister thanks the committee for their thorough work, and he fully respects the decision of the house on this matter. He’s made clear it was rightly a matter for parliament and not the government.” Questioned repeatedly, the spokesperson declined to say if Sunak agreed with the committee’s conclusion that Johnson had misled MPs. “He respects the decision the house has come to,” he said. “This follows extensive work by the committee, but beyond that, I don’t have any more to add.” He also declined to comment on how Sunak may have voted had he attended, saying: “I wouldn’t get into how he may have voted if he was there. Obviously, that is the definition of a hypothetical.” Asked if Sunak’s stance showed a lack of backbone, the spokesperson replied: “It was right to enable a free vote to ensure the house could come to a collective view, and he respects that view.” No 10 also refused to endorse comments by Penny Mordaunt, the Commons leader, who opened Monday’s debate by saying Johnson had presided over a “debasement of the honours system” with his resignation honours list. Asked if Mordaunt was speaking for the government, Sunak’s spokesperson said: “You’ve got our position on the former prime ministers’ honours system. I’m not aware of when the leader of the house made those comments, but I’m not aware of any plans to change our approach.” Mordaunt voted to endorse the report, as did ministers including Gillian Keegan, the education secretary, and Alex Chalk, the justice secretary. Angela Rayner, Labour’s deputy leader, said: “It’s astonishing that a prime minister who promised integrity, professionalism and accountability still doesn’t have an opinion about his disgraced predecessor being found guilty of repeatedly lying to parliament. Instead of turning the page on Boris Johnson, Rishi Sunak is showing just how weak and indecisive he is.” Christine Jardine, the Liberal Democrats’ Cabinet Office spokesperson, said: “Rishi Sunak is in complete denial over the Boris Johnson saga. The British public will rightly judge him for skipping the vote and not even offering an opinion.”