Police are investigating 12 parties in Downing Street and Whitehall, including a birthday gathering for Boris Johnson, according to Sue Gray's report.
The top civil servant revealed she was looking at 16 events in her partygate probe - and 12 of those are being examined by the Metropolitan Police.
Scotland Yard revealed it had been handed 300 pictures and 500 pieces of paper for its probe - and people involved would be contacted by police within weeks.
Ms Gray confirmed that cops are examining a birthday gathering on 19 June 2020 in the Cabinet room, where the PM was surprised by a cake.
His wife Carrie Johnson is said to have led staff in a chorus of "Happy Birthday".
Scotland Yard is also looking at the BYOB bash in the Downing Street garden on May 20 2020, which the Prime Minister was at.
He previously apologised in the Commons for attending the gathering for 25 minutes - but tried to claim he thought it was a work event.
Police are also looking at an alleged event in the Prime Minister's own flat on the night his aide Dominic Cummings quit.
The event, first reported by the Mirror but denied by No 10, took place on November 13 2020, during a national lockdown.
Sources told the Mirror that No10 aides “drank their socks off" and staff reported hearing "loud music pumping out of the flat" late into the night.
It has since been reported that allies of Mrs Johnson blasted out Abba's "The Winner Takes it All" following the departure of her rival Mr Cummings.
A separate leaving do for Mr Johnson's spin doctor Lee Cain on the same night is being examined by cops, the report states.
Police are also considering three events on December 17 - a Christmas quiz in Cabinet Secretary Simon Case, a send off for Kate Josephs, the former Director General of the Covid Taskforce, and another gathering for the departure of a No 10 official which has never been reported.
The Downing Street Christmas bash on December 18, first revealed by the Mirror, is being probed.
A new allegation about a leaving do for two No 10 private secretary on January 14 2021 is being considered.
And two boozy Downing Street leaving drinks on the eve on the Prince Philip's funeral in April 2021 are being probed.
Met Police Commander Catherine Roper said people involved would be contacted within weeks, with the investigation focusing on individual breaches of Covid rules.
"We had a bundle of material provided to us just Friday which is well over 500 pieces of paper, about a ream and a half, and over 300 photographs," she said.
"We'll be contacting those people that we want to have further information from with a series of questions - that could be via email or it could be by post."
In her report, Ms Gray blasted a "failure of leadership" and said "a number of these gatherings should not have been allowed to take place or to develop in the way that they did".
But her 12-page report was short on detail, as she said it was "not possible at present to provide a meaningful report" setting out all she discovered, due to the ongoing police investigation.
Only four events do not meet Scotland Yard's threshold for investigation, including a gathering in the Downing Street garden on May 15 2020 where the PM and staff were pictured enjoying cheese and wine.
A leaving do on November 27 2020 for special adviser Cleo Watson, a Christmas drinks at the Department for Education on 10 December 2020 and a No10 Christmas quiz on 15 December 2020 will also be left out of the police inquiry.
