The British Prime Minister may have attended as many as six events that are being looked into by police, according to reports.
A "bring your own booze party" attended by Boris Johnson during the first Covid lockdown and a gathering to mark his birthday are among 12 parties being investigated.
Further details have since been reported, suggesting the Conservative Party leader was seen heading to a party in his No 11 residence the night his former senior aide Dominic Cummings departed, and that he briefly attended a leaving do for one of his former defence advisers.
In her report, senior Cabinet Office official Sue Gray said just four of the 16 events which she looked into are not subject to Metropolitan Police inquiries.
The parties being investigated by the Met are:
20 May 2020: Bring Your Own Booze party
A leaked email from the Prime Minister's principal private secretary Martin Reynolds showed No 10 staff were invited to "bring your own booze" to an event in the Downing Street garden.
Mr Johnson has admitted he was there for 25 minutes, but said he thought it was a "work event" to thank staff for their efforts during the pandemic.
18 June 2020: Cabinet Office leaving do
Ms Gray's interim report said a gathering in the 70 Whitehall building was held to mark the departure of a No 10 private secretary.
The event had not previously been disclosed but the Telegraph said the official in question is former home affairs policy adviser Hannah Young, who left Downing Street to take up the role of deputy consul general in New York.
The newspaper said it understood about 20 people attended, with alcohol consumed.
19 June 2020: Boris Johnson's 56th birthday
Downing Street has admitted staff "gathered briefly" in the Cabinet Room in what was reportedly a surprise get-together for the Prime Minister organised by his now wife Carrie Symonds.
The PA news agency was told Lulu Lytle, the interior designer behind lavish renovations of the Downing Street flat, briefly attended while undertaking work there.
However, No 10 has denied a report that, later the same evening, family and friends were hosted upstairs to celebrate the occasion.
13 November 2020: Downing Street flat do
Ms Symonds reportedly hosted parties in the official flat over No 11 where she and Mr Johnson live, including one event on 13 November, the night of Dominic Cummings' acrimonious departure.
A spokesman for Ms Symonds called the claim "total nonsense".
But reports have since suggested that the Prime Minister was seen heading up to the flat on the night in question, with the Mail On Sunday stating that Abba songs, including The Winner Takes It All, were heard coming from the residence.
Mr Cummings, former de facto chief-of-staff at No 10, has alleged there are photographs of parties held at the flat during lockdown and said he has spoken to people who heard music coming from the Johnsons' accommodation on the night he exited Downing Street.
13 November 2020: Leaving party for senior aide
According to reports at the time, Mr Johnson gave a leaving speech for Lee Cain, his departing director of communications and a close ally of Mr Cummings.
17 December 2020: Cabinet Office "Christmas party"
The Cabinet Secretary Simon Case removed himself from the inquiry into Whitehall parties - to be replaced by Ms Gray - after reports emerged of a gathering in the Cabinet Office.
It was reported the do had been organised by a private secretary in Mr Case's team, and that it was included in digital calendars as: "Christmas party!" and included an online quiz.
The Cabinet Office said Mr Case played no part in the event "but walked through the team's office on the way to his own".
17 December 2020: Leaving drinks for former Covid Taskforce head
The former director-general of the Government's Covid Taskforce Kate Josephs said she was "truly sorry" over leaving drinks held in the Cabinet Office.
17 December 2020: No 10 leaving do
A leaving do was held for a departing Downing Street official.
The Telegraph reported that the staff member in question is Captain Steve Higham, then one of Mr Johnson's private secretaries, who advised on defence and national security issues.
The Mirror, which first reported the event before the police investigation began, said Mr Johnson was only there "for a few minutes".
Capt Higham became Commanding Officer of the aircraft carrier HMS Prince of Wales in July 2021.
18 December 2020: Downing Street Christmas party
Officials and advisers reportedly 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's spokeswoman Allegra Stratton resigned after video emerged of her joking about a "fictional party" at a mock press conference.
14 January 2021: More Downing Street leaving drinks
A gathering was held in No 10 to mark the departure of two private secretaries.
Reports have suggested the Prime Minister attended the leaving event, which was for a senior civil servant in the Department for Digital, Culture, Media and Sport, according to the Telegraph.
The other official's identity is so far unknown.
16 April 2021: Leaving drinks on the eve of the Duke of Edinburgh's funeral
The night before Britain's Queen Elizabeth II sat alone at the funeral of her husband of almost 70 years, in compliance with Covid rules at the time, two leaving dos were reportedly held in No 10.
Downing Street apologised to Buckingham Palace after reported details emerged of boozy drinks parties, including one for outgoing communications director James Slack.
Events not subject to police investigation:
15 May 2020: Cheese and wine in the No 10 garden
A photograph emerged of a number of groups gathered in the No 10 garden, including Mr Johnson, Ms Symonds, Mr Cummings and Mr Reynolds sitting together on the terrace.
27 November 2020: Another special adviser leaves
Mr Johnson reportedly gave a leaving speech at a gathering for Cleo Watson, another ally of Mr Cummings.
10 December 2020: Department for Education Christmas drinks
Then education secretary Gavin Williamson reportedly threw a party and delivered a short speech at his department's Whitehall headquarters.
15 December 2020: An online Christmas quiz in No 10
The Prime Minister appeared on contestants' screens at the quiz but insisted he broke no rules.
