LONDON -- Even as British Prime Minister Boris Johnson prepares to step down, the debate over his conduct in office is heating up.

Johnson on Friday released a government-commissioned legal opinion arguing that a parliamentary inquiry into the so-called Partygate scandal is unfair and "fundamentally flawed."

The opinion comes as a panel of lawmakers prepares to begin hearing testimony on whether Johnson misled Parliament when he repeatedly denied that staffers held a series of parties in his Downing Street offices in violation of COVID-19 lockdown rules. London's Metropolitan Police Service eventually issued 126 fines for breaches of the rules at eight events held at government offices in 2020 and 2021, including one to Johnson himself.

While the inquiry may seem arcane, it could prove a major setback for Johnson, who will remain a member of Parliament after he steps down as prime minister on Tuesday. If Johnson is found in contempt of Parliament he could be suspended from the House of Commons and face a recall election, threatening his position in the Conservative Party amid suggestions he would like to make another run at the prime minister's post.

Johnson's supporters argue that the House of Commons Committee of Privileges, which will conduct the inquiry, has changed the rules to ensure Johnson will be found in contempt. While government ministers have traditionally faced censure only if they "knowingly" mislead lawmakers, the panel has decided that intent no longer matters, they say.

The opinion from David Pannick, an expert in constitutional law and human rights, and Jason Pobjoy from Blackstone Chambers in London, supports that position.

"The Committee has failed to understand that to prove contempt against Mr. Johnson, it is necessary to establish that he intended to mislead the House," they said. "The threat of contempt proceedings for unintentional mistakes would have a seriously chilling effect on all members."'

But the committee says it hasn't changed the rules, and Johnson's supporters are misrepresenting the rules on ministerial conduct and the panel's inquiry.

The panel said in July that its first job would be to determine whether Johnson's statements obstructed or impeded the work of Parliament, regardless of whether that was done intentionally. The question of intent will be considered when the committee decides what punishment to recommend.

If the committee finds Johnson in contempt, it could recommend punishments ranging from an oral apology to suspension or even expulsion from Parliament, or it could recommend no sanction at all. Any punishment would have to be approved by the House of Commons.

Chris Bryant, an opposition Labour Party lawmaker who chairs the Privileges Committee but has recused himself from the inquiry, dismissed Pannick's opinion as "disgraceful bullying."

"You would have thought that Boris Johnson would want to clear his name in front of the Privileges Committee instead of trying to intimidate it," he wrote in a series of tweets. "There is no danger of ministers being cowed by this inquiry -- although of course it would be good if they were careful that what they say to Parliament is true and accurate -- as the House will always recognize an honest mistake quickly corrected."