Boris Johnson has sworn "hand on heart, I did not lie to the House" as he was questioned by MPs over whether he misled the Commons with his denials of partygate in a hearing that could determine his political fate.
Harriet Harman, the chair of the Privileges Committee undertaking the grilling, rejected the former prime minister's demand that the inquiry only considers his discussion of coronavirus guidance.
The Labour grandee said the MPs on the cross-party committee will leave their "party interests at the door of the committee room and conduct our work in the interests of the House" as she dismissed claims of bias.
She insisted the committee is "not relying" on evidence provided by the Sue Gray report, as allies of Mr Johnson claim the inquiry is a "witch hunt" now that the civil servant is joining Labour leader Sir Keir Starmer's office.
Ms Harman added: "We have not changed the rules of the procedure that is not within our remit, that is laid down by the House, we're bound to follow them, that is not what we've done."
She said the evidence raises "clear questions and this is Mr Johnson's opportunity to give us his answers" before asking him to take the oath.
He swore to tell the truth before issuing an apology and adding "hand on heart, I did not lie to the House".
Boris Johnson continued: "When this inquiry was set up I was completely confident that you would find nothing to show that I knew or believed anything else, as indeed you have not.
"I was confident, not because there has been some kind of cover-up. I was confident because I knew that was what I believed and that is why I said it."
The former prime minister said there was a "near universal belief at No 10 that the rules and the guidance were being complied with".
"That is the general belief that has been uncovered by your evidence, and it was that belief that governed what I said in the House," he added.
"As soon as it was clear I was wrong and as soon as the Sue Gray investigation and the Metropolitan Police investigation had concluded, I came to the House of Commons and I corrected the record as I promised I would.
"I clearly could not have anticipated the outcome by coming earlier, because I genuinely did not know what the outcome would be."
