Boris Johnson could be forced to face a byelection in his Uxbridge constituency if he is found to have misled MPs over Partygate, a report from the House of Commons privileges committee has made clear.

Despite having resigned as Conservative leader, Johnson still faces a parliamentary probe over whether he misled MPs when he told them repeatedly that “all guidance was followed” in Downing Street during the pandemic – something subsequently proved to be untrue.

The committee, which will start taking oral evidence in the autumn, including from the prime minister, published a report on Thursday setting out how it will carry out its inquiry – including the fact that, as previously reported, witnesses will be questioned under oath.

The committee has obtained a ruling from the Speaker, Lindsay Hoyle, confirming that if Johnson is found to have been in contempt of parliament, and the committee punishes him with a suspension from the House of Commons, that could trigger the Recall Act.

This legislation means MPs suspended from parliament for 10 days or more – or sentenced to imprisonment – can face a byelection, if 10% of voters in their constituency sign a petition demanding one.

MPs would have to vote to confirm the suspension, but Johnson could face a humiliating petition, and if local Conservatives allowed him to stand again, the prospect of losing his seat.

Former Labour MP Fiona Onasanya was removed following such a petition after she was found to have lied to police over a speeding ticket.

Johnson tried to avoid a suspension – which could have led to a byelection – for veteran MP Owen Paterson over paid lobbying, sparking a furious backlash from colleagues.

As well as confirming the potential sanctions against Johnson, the privileges committee also makes clear that it could take evidence from some witnesses in private.

And it spells out legal advice it has received from House of Commons clerks, making clear Johnson does not have to have deliberately misled MPs to be found to have misled the House, and therefore to have held the Commons in contempt.

“Looking at contempt in broad terms, intention is not necessary for a contempt to be committed. The Clerk’s memo explains that while ‘much of the commentary has focused on whether Mr Johnson “deliberately” or “knowingly” misled the Committee’, this wording is not in the motion,” the committee’s report says.

In a further suggestion Johnson faces a challenge to avoid being sanctioned, the committee also makes clear that it will be making its judgment “on the balance of probabilities”.