Apologising in the House of Commons this afternoon, the Prime Minister said he could see the public “rage” over the incident in May 2020, but that he thought the gathering was a “work event”.
Labour have now called on Mr Johnson to resign.
Mr Johnson told MPs that he attended the May 20 2020 gathering for around 25 minutes to “thank groups of staff”.
“I believed implicitly that this was a work event,” he said.
But “with hindsight I should have sent everyone back inside, I should have found some other way to thank them, and I should have recognised that – even if it could have been said technically to fall within the guidance – there would be millions and millions of people who simply would not see it that way.”
Mr Johnson acknowledged that included “people who have suffered terribly, people who were forbidden for meeting loved ones at all inside or outside” adding: “To them and to this House, I offer my heartfelt apologies.”
Sir Keir Starmer took to his feet after the apology, and used his weekly round of questions to the leader opposite to tell him to leave office.
After months of deceit and deception, the pathetic spectacle of a man who has run out of road,” Sir Keir said.
“His defence … that he didn’t realise he was at a party is so ridiculous that it’s actually offensive to the British public.”
He added: “The party’s over, Prime Minister. The only question is will the British public kick him out, will his party kick him out or will he do the decent thing and resign?”
Yorkshire MPs were among those standing to criticise Mr Johnson, during a questions session that was standing room only in the House of Commons.
Kingston Upon Hull East’s Karl Turner said that Mr Johnson was not sorry for having attended the gathering, but only that he has “been caught”.