A defiant Boris Johnson is preparing an extraordinary televised defence of his actions during the Partygate scandal, as his allies this weekend accused the parliamentary inquiry into the affair of relying on weak evidence compiled by a former civil servant recruited by the Labour party. With a potentially explosive appearance at the Commons privileges committee due on Wednesday, the Observer can reveal that the former PM’s legal team intends to publish written evidence, including new witness statements, supporting Johnson’s claim that he did not knowingly mislead MPs over lockdown parties – as well as examples of the advice he was given at the time. The document, overseen by his lead counsel David Pannick, is set to be published before Wednesday’s five-hour hearing. It is expected to warn the cross-party committee that it will effectively be ripping up parliamentary precedent should it sanction Johnson, who, the document will say, gave his honest views at the time and corrected the record when he learned of wrongdoing. His allies also argue that the committee’s interim report, which found there was significant evidence he misled MPs over lockdown parties, referred extensively to an earlier Partygate investigation led by the former senior civil servant Sue Gray. She has since been recruited as Keir Starmer’s chief of staff, although has yet to start in the post. Johnson’s allies argue that Gray’s report is mentioned more than 30 times in the interim report and that it supplied the “core evidential basis” of the committee’s work. The committee insists, however, that all the evidence it has amassed has been compiled entirely independently from the investigations conducted by Gray. Committee sources say that Johnson has already been provided with the “full stack” of uncensored evidence it has compiled during its investigations over the last 10 months, including 23 witness statements, with the names of the people who gave them. Most of the names were not published in the interim report earlier this month, which instead referred to No 10 officials and others without specifying who most of them were. All the statements provided to the committee were taken under “oaths of honesty”. Johnson has also been sent WhatsApp messages and other evidence supplied to the committee by the government, as well as photographs of gatherings, including ones he attended. A committee source said: “He has got everything that the committee has including all the names.” There is also speculation this weekend that Johnson may be using his resignation honours list to reward those who have helped him through the inquiry – an allegation his team rejects as “completely untrue”. The Observer has been told that several figures who have featured in the inquiry also appeared in the draft version of Johnson’s honours list. They include Martin Reynolds, his former principal private secretary, who sent a widely shared email urging staff to “bring your own booze” to one event on 20 May 2020. Others include former chief of staff Dan Rosenfield, as well as media advisers Jack Doyle and Guto Harri. Also said to have been in his original list is former home secretary Priti Patel. She said last week that there was a “culture of collusion” around the privileges committee inquiry, and that members of it had already been critical of Johnson. Wendy Chamberlain, the Liberal Democrat chief whip, said: “Boris Johnson’s honours list is nothing more than a reward for his failure, lies and corruption. No prime minister, let alone one who disgraced himself as Johnson did, should be able to use the honours list for their own gain. The allegation of key figures being strategically chosen to help Johnson through the inquiry must be urgently investigated. Sunak must not allow Boris Johnson to continue poisoning the well of British politics.” Johnson allies say they are now “very confident” that he can prove that he did not knowingly mislead the House of Commons over what has become known as Partygate. They believe that he can prove that he received civil service advice before telling MPs in December 2020 that no rules were broken in Downing Street. His written evidence will also claim that, when he discovered rules had been broken, he corrected the record. A spokesperson for Johnson said: “The committee will vindicate Boris Johnson’s position. The evidence will show that Boris Johnson did not knowingly mislead parliament. Despite a 10-month investigation, the privileges committee has not produced a single piece of evidence showing Boris Johnson knowingly misled parliament. The committee will exonerate Boris Johnson of any contempt of parliament.” On Wednesday the seven committee members (four Conservative MPs, two Labour and one SNP) will meet at 1.30pm until 2pm to prepare to question Johnson, before the main hearing starts. A Commons committee room has been booked from 2pm until 7pm, with the entire session being televised. The committee is expected to home in on why Johnson was unaware that the parties he attended breached the same Covid rules he was telling the country to obey in daily press briefings. The MPs will also want to know why, having made statements to parliament insisting no rules were broken, he did not return earlier and more regularly to correct the record. The committee chair, Harriet Harman, will open the session, before Johnson is expected to make initial remarks and swear an oath of honesty, before all MPs are given time to ask questions. Johnson will bring his lawyer, Lord Pannick, but he will not be able to answer questions on his behalf. However, Johnson will be able to turn to him for advice during the hearing or before answering questions himself. Sources close to the committee said Johnson would not be wise to repeat accusations made recently in his name by his spokesman, that Gray’s appointment as Starmer’s chief of staff showed the whole inquiry process was a “political show trial with an outrageous level of bias”. The committee’s damning interim report early this month included comments from one witness saying the then prime minister told a packed No 10 gathering in November 2020, when strict Covid restrictions were in force, that “this is probably the most unsocially distanced gathering in the UK right now”. It also included comments from a No 10 official in April 2021, six months before the first reports of parties emerged, saying a colleague was “worried about leaks of PM having a piss-up – and to be fair I don’t think it’s unwarranted”. If the committee finds that Johnson misled parliament, it could lead to his suspension, if the committee finding is approved in a vote of the House of Commons. Under parliamentary rules, an exclusion of 10 days or longer would mean Johnson’s constituents could seek a recall petition to remove him as their MP. Last week he was reselected as the MP for Uxbridge and South Ruislip.