0538 GMT May 26, 2022
Johnson, who in 2019 won the biggest Conservative majority in more than 30 years, is braced for the publication of an official investigation into claims that there were multiple Downing Street parties during lockdowns. He told Parliament no rules were broken, Reuters reported.
It was not immediately clear when the results of that investigation by Cabinet Office official Sue Gray would be published, especially as police have opened their own investigation.
Asked by the opposition Labour Party leader Keir Starmer if the ministerial code, which says that ministers who had knowingly misled Parliament should offer to resign, applied to him Johnson said: "Of course".
"If he'd misled Parliament, he must resign," Starmer told Parliament. "Will you now resign?"
He said he could not speak about investigations into the alleged parties. Johnson said his government was focused on driving economic growth and leading the Western response to the Ukraine crisis.
Johnson has given a variety of explanations about the parties: First he said no rules had been broken but then he apologised to the British people for the apparent hypocrisy of such gatherings.
He has denied an allegation he was warned that a lockdown gathering on May 20, 2020, which he says he thought was a work event, was inappropriate.
ITV reported on Monday that Johnson and his now wife Carrie had attended a surprise party of up to 30 people for his birthday in the Cabinet Room at Downing Street in June 2020, when indoor gatherings were banned.
British police on Tuesday said they had opened their own investigation into lockdown events at Downing Street, upping the pressure on Johnson.
Some of his lawmakers have already demanded he resign but to trigger a leadership challenge, 54 of the 359 Conservative MPs in Parliament must write letters of no confidence to the chairman of the party's 1922 committee.
The number of letters submitted is kept secret until the threshold of 54 is reached.
British Foreign Secretary Liz Truss, tipped as a possible future prime minister if Johnson is toppled, said Downing Street had not yet been given the findings of the Gray report but that it would come out very soon.