This is not the first time Boris Johnson has faced criticism over rule-busting gatherings said to have occurred during the pandemic.
And on Tuesday, he said he believed a gathering in No 10's garden during the first lockdown was a "work event" after being accused of lying to Parliament by Dominic Cummings.
Here is what the Prime Minister has said in response to the claims which have been made.
May 15 2020: Garden party at Downing Street (cheese and wine)
In December 2021, a photo emerged showing Boris and Carrie Johnson, former chief adviser Dominic Cummings, and Mr Johnson's principal private secretary, Martin Reynolds, sitting around a table in the No 10 garden during the first national lockdown.
Mr Johnson said in an interview on December 20 2021: "Those were meetings of people at work. This is where I live and it's where I work. Those were meetings of people at work, talking about work."
May 20 2020: Garden party at Downing Street (BYOB)
An email, leaked to ITV, from Mr Reynolds to more than 100 Downing Street employees asked them to "bring your own booze" for an evening gathering.
The Prime Minister has admitted attending for 25 minutes but insisted he thought the gathering was a work event, and No 10 has said Mr Johnson did not know about the event beforehand.
But his former chief aide Dominic Cummings said this was not true, and he had warned it was against the rules.
Mr Johnson said during a visit to the Finchley Memorial Hospital in north London on Tuesday: "I want to begin by repeating my apologies to everybody for the misjudgments that I've made, that we may have made in No 10 and beyond, whether in Downing Street or throughout the pandemic.
"Nobody told me that what we were doing was against the rules, that the event in question was something that ... was not a work event, and as I said in the House of Commons, when I went out into that garden I thought that I was attending a work event."
He said: "I can tell you categorically, categorically, that nobody told me and nobody said that this was something that was against the rules or was a breach of the Covid rules or we were doing something that wasn't a work event because, frankly, I don't think, I can't imagine why on earth it would have gone ahead or why it would have been allowed to go ahead."
November 13 2020: Leaving party for senior aide and Johnsons' flat party
According to reports at the time, Mr Johnson gave a leaving speech for Lee Cain, his departing director of communications and close ally of Mr Cummings.
There are also allegations that the Prime Minister's then-fiancee hosted parties in their flat, with one such event said to have taken place on November 13 2020, the night Mr Cummings departed No 10.
Mr Johnson was asked in the House of Commons on December 8 2021: "Will the Prime Minister tell the House whether there was a party in Downing Street on November 13?"
He replied: "No, but I'm sure that whatever happened the guidance was followed and the rules were followed at all times."
December 15 2020: Downing Street quiz
The Sunday Mirror published an image in December 2021 showing the Prime Minister flanked by colleagues, one draped in tinsel and another wearing a Santa hat, in No 10 the previous year.
Downing Street admitted Mr Johnson "briefly" attended the quiz after photographic evidence emerged, but insisted it was a virtual event.
In an interview on December 13 2021, the Prime Minister said: "I can tell you that I certainly broke no rules - the whole thing will be looked into by the Cabinet Secretary, and what I'm focused on, frankly, is the vaccine rollout."
December 18 2020: Christmas party at Downing Street
According to reports which first emerged at the end of November 2021, officials and advisers made speeches, enjoyed a cheese board, drank together and exchanged Secret Santa gifts - although the Prime Minister is not thought to have attended.
Mr Johnson said in an interview on December 7 2021: "I have satisfied myself that the guidelines were followed at all times."
He said in the House of Commons on December 8 2021: "I repeat that I have been repeatedly assured since these allegations emerged that there was no party and that no Covid rules were broken. That is what I have been repeatedly assured.
"But I have asked the Cabinet Secretary to establish all the facts and to report back as soon as possible. It goes without saying that if those rules were broken, there will be disciplinary action for all those involved."
The Prime Minister also said in the Commons on December 8 2021: "I apologise for the impression that has been given that staff in Downing Street take this less than seriously. I am sickened myself and furious about that, but I repeat what I have said to him: I have been repeatedly assured that the rules were not broken."
April 16 2021: Leaving parties night before Duke of Edinburgh's funeral
The Telegraph reported that advisers and civil servants gathered after work for two separate events on April 16 2021, as the country was in a period of mourning after the death of the Duke of Edinburgh.
One was for former Downing Street director of communications James Slack and the second for a photographer, and they were later reported to have merged.
The following day, the Queen sat alone - socially distanced from her family - as she mourned her husband.
No 10 previously said an apology had been extended to Buckingham Palace.
And Mr Johnson said: "I deeply and bitterly regret that that happened."
He said: "I can only renew my apologies both to Her Majesty and to the country for misjudgments that were made, and for which I take full responsibility."