MPs investigating Boris Johnson over his Partygate denials are not expected to release their final report on whether he misled parliament until next month at the earliest, the Guardian has been told. After the former prime minister submitted what was termed a “bombshell” 50-page dossier laying out his defence on Monday afternoon, sources suggested a verdict by the privileges committee would come after Easter. With the Commons in recess until 17 April and local elections several weeks later, which the committee would not want to be accused of influencing, sources indicated a ruling may not be made until May. When the final report is drawn up, Johnson will also be given two weeks to review it and respond. There are concerns that if the committee finds he did mislead parliament, then Johnson could use this period to build a campaign against it. Taxpayer-funded legal support for Johnson is set to last until 30 April, and the Guardian understands the privileges committee intends for its inquiry to be completed before the summer. However, there are questions over how much closer towards the summer a vote on any potential sanction would come. While Johnson is the only witness that the committee has called to be questioned at a public hearing, a source suggested he could be summoned back again if there was a need to ask him further questions in person. Johnson’s defence dossier is said to contain new evidence that the privileges committee has not yet published. It reportedly contains a message from Jack Doyle, the former prime minister’s then director of communications, showing Johnson was given a “line to take” that no rules were broken that he later relied on when giving the same assurance in parliament. A source close to him stressed they were cooperating with the committee and added: “We have nothing to hide.” Legal advisers and Commons officials were combing through the dossier “in the interests of making appropriate redactions to protect the identity of some witnesses”, a spokesperson for the committee said. They added: “The committee intends to publish this as soon as is practicably possible.” As Johnson’s allies escalated attacks on the inquiry, Downing Street defended the cross-party group of seven MPs who have been investigating the issue of whether he misled parliament for around 10 months. Rishi Sunak’s spokesperson pointed to a defence of the committee by Penny Mordaunt, the leader of the Commons, saying she had set out “how parliamentarians should engage” with the process. Last week, Mordaunt told MPs that attacks on the committee were “a very serious matter” and its members were “doing this house a service”. She added those running the inquiry should be “permitted to get on with their work without fear or favour”, and that a “very dim view will be taken of any member who tries to prevent the committee from carrying out this serious work”. No 10 also denied reports that announcements on pensions, energy and crime had been pushed back due to concerns that Johnson’s showdown with the committee would overshadow them. Sunak’s spokesperson insisted it was “wrong to say that government business changed” as a result of the timing of the hearing. One of Johnson’s closest allies, his fellow Tory MP Conor Burns, suggested there were concerns about the impartiality of the Labour chair of the privileges committee, Harriet Harman. He told the BBC: “I rate Harriet Harman highly, but she did tweet in April 2022 that if [Johnson and Sunak] admit guilt, by which she said was accepting a fixed-penalty notice, then they are also admitting that they misled the House of Commons. “Boris Johnson contests that, but it seems to me the person who is chairing this committee has predetermined it and that causes me a degree of anxiety for parliament’s reputation in handling this with integrity.” Alexander Horne, a former legal adviser to parliament, said that some attacks by Johnson’s supporters – including calling the privileges committee a “kangaroo court” – could themselves constitute contempt of parliament. Robert Hayward, a Tory peer and elections expert, also suggested an attempt at a comeback by Johnson would not go down down well. He said on Monday that another Tory leadership contest “would be an utter joke”. If the privileges committee finds Johnson misled MPs, it could recommend a suspension from the Commons. A ban of 10 days or more could trigger a recall petition in Johnson’s constituency, and result in him being ejected from parliament. MPs will get a free vote on whether to approve any suspension.