“Mr Speaker, I want to apologise,” he told a packed Commons. “I know that millions of people across this country have made extraordinary sacrifices over the last 18 months. I know the anguish that they have been through, unable to mourn their relatives, unable to live their lives as they want or to do the things they love.”

He said: “I know the rage they feel with me, and with the government I lead, when they think that in Downing Street itself the rules were not being properly followed by the people who make the rules.”

Johnson said that on the evening concerned he joined the event for about 25 minutes from around 6pm, saying that, with the No 10 garden being used as “an extension of the office” amid lockdown, he believed it was a work event.

“With hindsight I should have sent everyone back inside,” Johnson added, while arguing that the event “could be said, technically, to fall within the guidance” of the time.