If the committee finds he deliberately misled lawmakers, then he could be suspended. Any suspension longer than 10 days could prompt an election to remove him from his parliamentary seat.

The former leader, who considered an audacious bid for a second stint as prime minister last year, launched a lengthy defence at the hearing today, saying statements he made to parliament had been done in good faith.

"I'm here to say to you, hand on heart, that I did not lie to the House," said Mr Johnson, who has accused the committee of bias.

"When those statements were made. They were made in good faith and on the basis of what I honestly knew and believed at the time."

The so-called partygate scandal contributed to the ultimate downfall of Mr Johnson, after months of reports that he, alongside other senior government figures, had been present at alcohol-fuelled gatherings in Downing Street during 2020 and 2021 when much of the rest of Britain was forced to stay at home.

Mr Johnson was fined by police for attending an event to celebrate his birthday in Downing Street in June 2020, making him the first prime minister found to have broken the law while in office.

The outcry and repeated allegations of lying over the over parties and allegations that a Conservative lawmaker had drunkenly groped two men eventually prompted the resignations of most of his top team of government ministers, including the current Prime Minister, Rishi Sunak.

Harriet Harman, the chair of the committee, stressed the importance of ministers telling the truth, saying this went to the heart of the way Britain's parliamentary system functions.

"Misleading the house might sound like a technical issue, but it is a matter of great importance," she said.

At the start of the hearing, Mr Johnson was made to swear an oath to tell the truth on a bible before giving his evidence.

He said the inquiry had not found any evidence he deliberately misled parliament and said he was banned by the committee from publishing a "large number of extracts" he relied on in his defence.

He denied it would have been "obvious" to him that he had broken rules or guidance, adding that no officials had raised any concerns with him.

If so, it would have been obvious to everyone else there "including the current prime minister", he said, referring to Mr Sunak. "On the contrary, the overwhelming evidence which you have assembled, is that these individuals believe that the rules and the guidance were being complied with," he said.

Earlier on Wednesday, the committee published 110 pages of evidence, showing that some Downing Street officials said Mr Johnson must have known that parties had taken place despite his denials.

In the new evidence, the cabinet secretary Simon Case said he had never given Mr Johnson any assurances that Covid rules had been followed in Downing Street - and that he did not know any officials who did either.

Another Downing Street aide said Mr Johnson had the opportunity to "shut down" the parties, but he instead joined in making speeches and drinking with staff.

"I apologise for inadvertently misleading this house," Mr Johnson said. "But to say that I did it recklessly or deliberately is completely untrue, as the evidence shows."