Boris Johnson has apologized for attending a gathering in the back garden of 10 Downing Street on May 20, 2020, at which point Britons were prohibited from gathering due to strict coronavirus restrictions.

At the start of the weekly session of Prime Minister's Questions, Johnson said he did attend the gathering for 25 minutes before going inside to work. He said he believed the gathering to be a work event, but with hindsight conceded he should have sent attendees back inside.

Leader of the opposition Keir Starmer said the UK Prime Minister's excuse that he "did not realize he was at a party" was ridiculous and "offensive." The Labour Party leader went on to ask if the Prime Minister would resign.

The Prime Minister's comments on Wednesday came after days of outrage over a "bring your own booze" event held at Downing Street during the height of the UK's first Covid-19 lockdown.

On Monday night, it emerged that his principal private secretary, Martin Reynolds, had emailed an invitation to more than 100 Downing Street staffers to "socially distanced drinks in the No. 10 garden" on May 20.

The email, which has been independently confirmed by CNN, told guests to "bring your own booze" and "make the most of the lovely weather."

This happened while the UK was in a hard lockdown to combat the spread of Covid-19. At the time, people in England were banned from meeting with more than one other person outdoors, and would be legally punished for doing so. In workplaces, official guidance stated that in-person meetings should only take place if "absolutely necessary."

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Johnson had refused to deny reports that he and his wife, Carrie Johnson, attended the event. He said he would not comment further, as there is an ongoing inquiry into parties in Downing Street.

If a government minister breaches the ministerial code, it is expected that they should resign from their job.

Members of Johnson's own Conservative party have already come out strongly, with the leader of the Scottish Conservatives saying Johnson must resign if it transpired he attended these drinks.

The May 20 allegation comes after a string of scandals questioning precisely how fit Johnson is for office. The scandals range from an attempt to fix rules to prevent one of his Conservative allies -- who had broken lobbying rules -- from being suspended from Parliament, to handing lucrative Covid-19 contracts to people closely associated with the Conservative party.

Before Christmas, stories emerged of numerous drinks parties taking place in Downing Street during various stages of lockdown in the UK.

The bombshell allegations affected Johnson's poll ratings and as of this week, a majority of British citizens believe that if Johnson did attend the May 20 drinks party then he should resign as Prime Minister.