Boris Johnson could be forced to face a by-election if he is found to have lied to Parliament and is handed a suspension for 10 or more sitting days.
The Privileges Committee is examining whether the Prime Minister committed a contempt of Parliament by misleading MPs over the partygate scandal.
Commons Speaker Sir Lindsay Hoyle confirmed the committee’s findings would fall within the remit of the Recall of MPs Act, following advice from a leading lawyer.
That would mean a suspension of 10 or more sitting days, or 14 calendar days, would trigger a recall petition.
If at least 10% of voters in Mr Johnson’s Uxbridge and South Ruislip seat demand a by-election he would lose his place as an MP, but would be eligible to stand again in the contest.
The cross-party committee also published advice from the Clerk of the Journals, Eve Samson, the Commons’ expert on parliamentary privilege, which suggested that whether Mr Johnson intended to mislead MPs was not a factor that needed to be considered.
But she said intent could be seen as an “aggravating factor” when considering penalties.
In a report setting out how it will handle the case, the Privileges Committee said: “We agree with the reasoning about the nature of a contempt in that paper, namely that the focus of the House’s jurisdiction is on whether or not an action or omission obstructs or impedes or has a tendency to obstruct or impede the functioning of the House, with the consequence that, looking at contempt in broad terms, intention is not necessary for a contempt to be committed.”
The case will be considered “on the balance of probabilities” – a lower standard than the criminal test of “beyond reasonable doubt”.
The Privileges Committee also insisted its inquiry will go ahead despite Mr Johnson’s resignation as Tory leader and his expected departure from Number 10 in September.
“Since the House agreed the referral there have been political developments concerning the future role of the Rt Hon Boris Johnson, and some have suggested that the committee’s inquiry is no longer necessary,” the MPs said.
“Our inquiry, however, is into the question of whether the House was misled, and political developments are of no relevance to that.”
The MPs intend to call Mr Johnson to give oral evidence in public in the autumn, under oath.
The committee has already said that whistle-blowers will be able to give evidence about the Prime Minister anonymously.
Mr Johnson has also been ordered to hand over a cache of documents to the MPs investigating whether he lied to Parliament with his partygate denials.
The committee wrote to the Prime Minister and Cabinet Secretary Simon Case demanding details relevant to its inquiry.
Downing Street was unable to set out a response to the committee, nor could it say when it would be replying.
The Prime Minister’s official spokesman said: “As with previous letters from the committee, we will need to consider them and then set our response, this is a formal parliamentary process.”
Asked if Mr Johnson intends to co-operate with the inquiry, the spokesman said: “We have said we will assist the committee in their work but beyond that I will have to repeat again it will need to wait for the formal response.”
