Boris Johnson’s defence against claims he lied to Parliament over the partygate scandal could be published on Monday as he prepares for a showdown with MPs.

The Privileges Committee is expected to publish the lengthy submission from Mr Johnson’s barrister Lord Pannick KC before the former prime minister gives evidence on Wednesday in a session which could decide his political future.

An estimated £220,000 of taxpayers’ money has been allocated for Mr Johnson’s legal bills and allies insisted he expected his position to be “vindicated” after submitting a “detailed and compelling” account of his case.

The seven-member Privileges Committee, chaired by Labour’s Harriet Harman but with a Tory majority, will decide whether Mr Johnson misled the Commons with his denials of lockdown rule-breaking in No 10 at the height of the Covid-19 pandemic.

If the MPs believe he did mislead the House, they will consider whether it was “reckless or intentional” and amounted to a contempt of Parliament.

His lawyers have already queried the process being used by the Privileges Committee, including pushing for him to be legally represented at the hearing, arguing for a higher standard of proof than the balance of probabilities, and suggesting he must be shown to have intended to mislead Parliament for a contempt to have occurred.

After an interim report by the committee earlier this month said evidence strongly suggested breaches of coronavirus rules would have been “obvious” to the then-prime minister, Mr Johnson claimed it was “clear” that he had not committed a contempt of Parliament.

He said there was “no evidence in the report that I knowingly or recklessly misled Parliament” or failed to update it in a timely manner.

Mr Johnson has also sought to cast doubt on the findings of Sue Gray’s report on partygate, after she quit the civil service because she intends to take up a role as Labour leader Sir Keir Starmer’s chief of staff.

Allies of Mr Johnson claim that, despite his insistence he will be vindicated, the process against him could amount to a “witch hunt”.

They have also sought to cast doubt on the impartiality of Ms Harman after a social media post last year indicated she believed Mr Johnson had misled Parliament.

Former minister Conor Burns, an ally of Mr Johnson, said: “Boris Johnson’s contention is that what he told the House of Commons was, to the best information supplied to him, true when he told that to Parliament, and I welcome the fact that he is going to bring forward evidence to back up that.

“It’s not unusual, anyone who has appeared as a minister in the House of Commons knows that you rely very heavily on briefing that you’re given.”

On BBC Radio 4’s Westminster Hour he added: “I rate Harriet Harman highly, but she did tweet in April 2022 that if (Boris Johnson and Rishi 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.”

Mr Burns, who spoke to Mr Johnson on Sunday afternoon, said: “He is looking forward to the opportunity of getting his case out there, to putting his case to the committee on Wednesday, to answering their questions.”

Tory peer Lord Greenhalgh said he hopes the former prime minister gets a “fair and just hearing” but voiced concerns about the process.

The peer, who was a deputy mayor when Mr Johnson was in London’s City Hall and became a minister under him as prime minister, has backed a campaign for the four Conservative MPs on the committee to pull out of the “kangaroo court”.

He told Times Radio: “I’m concerned that it will be a witch hunt.”

Pressed on the Conservative Post campaign for the four Tories to pull out of the process, Lord Greenhalgh said: “I’m hoping as a parliamentarian that there will be fairness around this, that is my fervent hope.

“But if not, then the thing should not go ahead.”

Fellow Tory peer Lord Kirkhope warned against the “nonsense” of putting pressure on MPs on the committee.

Home Secretary Suella Braverman would not be drawn on the Privileges Committee process, but said she admired the former prime minister.

“Boris Johnson was a really important leader for our country – he got Brexit done, he delivered the Covid vaccine, and he led the UK support for Ukraine,” she said.

“For all of those things, I’ll be an admirer of his.”

Cabinet Office minister Oliver Dowden said he expected Mr Johnson to give a “robust defence” of his actions.

A spokesman for Mr Johnson said: “The Privileges Committee will vindicate Boris Johnson’s position.

“The evidence will show that Boris Johnson did not knowingly mislead Parliament.”

The Privileges Committee is examining evidence around at least four occasions when Mr Johnson may have misled MPs with his assurances to the Commons that lockdown rules were followed.

He is expected to highlight previously undisclosed WhatsApp messages from senior civil servants and members of his No 10 team showing he had relied on their advice when he made his statements to Parliament.

He will also publish messages which show other senior figures in Downing Street believed the gatherings were covered by the “workplace exemption” in the lockdown rules.

The committee will publish its findings on whether Mr Johnson committed a contempt of Parliament and make a recommendation on any punishment, but the ultimate decision will fall to the full House of Commons.

Prime Minister Rishi Sunak has said he will not seek to influence MPs on the committee and is expected to grant a free vote in the Commons on any sanction that may be recommended.

A suspension of 10 sitting days or more for Mr Johnson could ultimately trigger a by-election in his Uxbridge and South Ruislip seat, which he held with a majority of 7,210 in 2019.

Former chancellor Kwasi Kwarteng suggested the “hugely intelligent, sensitive, brilliant” Mr Johnson could mount a political comeback and return to lead the party.

He told GB News “he’s been written off so many times” but “he is someone who I would never rule out or count out”.