Boris Johnson and his Downing Street staff are accused of breaking strict Covid rules by attending parties at Number 10 last year in the run-up to Christmas.
The Prime Minister gave a speech at a packed leaving do for a top aide last November when the country was in lockdown for the second time, reports the Mirror.
Members of his top team then held their own festive bash in Downing Street just days before Christmas, while London was under tier 3 restrictions.
Officials are said to have knocked back glasses of wine during a Christmas quiz and a Secret Santa while the rest of the country was ordered to stay at home.
Around “40 or 50” people were said to have been crammed “cheek by jowl” into a medium-sized room in Number 10 for each of the two events.
“It was a Covid nightmare,” one source claimed.
It comes after top health chief Dr Jenny Harries warned that people should cut down on unnecessary social gatherings over the festive season to curb future Covid surges.
But Mr Johnson rejected the idea today that festive parties should be scrapped, adding: “We don’t want people to cancel such events.”
In explosive revelations, one source told the Mirror there were “many social gatherings” in Downing Street last year while the public faced restrictions.
They even claimed there were “always parties” in the flat the Prime Minister shares with his wife, adding: “Carrie’s addicted to them”.
There were also claims of a third, smaller gathering on November 13, the night Dominic Cummings walked out of No 10, "where they were all getting totally plastered".
Another source claimed: “While senior civil servants were urging caution and there was one message to the public, Prime Minister gave the impression that it could be very relaxed in No 10.
“He would either turn a blind eye or on some occasions attend himself while everyone else was in lockdown”.
The official No 10 staff Christmas party was cancelled with officials understood to have taken part in a Zoom quiz instead.
But the leaving do still took place on November 27 while the unofficial Christmas bash, which the PM did not attend, happened on December 18.
One legal expert has said the events could even have been punishable with a whopping £10,000 fine.
Downing Street did not deny the claims, but a spokesman said: “Covid rules have been followed at all times.”
A spokeswoman for Mrs Johnson denied she had held any parties at the flat while restrictions were in place, adding: “This is total nonsense.
"Mrs Johnson has followed coronavirus rules at all times and it is categorically untrue to suggest otherwise.”
Last November, Mr Johnson plunged England into its second national lockdown for four weeks with people asked to work from home and any indoor socialising banned.
London went into Tier 2 restrictions the following month - which prohibited households from mixing indoors.
The city - which had the highest Covid case rates in the country - then moved into Tier 3 on December 16, which banned all indoor mixing except in household bubbles.
The only feasible legal way for either gathering to have taken place was if it was "reasonably necessary for work" under the regulations.
Downing Street staff have been classified as key workers throughout the pandemic.
Their offices were set up to be Covid secure, with perspex screens between desks and hand sanitising stations.
The rule of six was regularly enforced in meetings and the number of people who were allowed to see the PM at any one time was strictly limited, while social distancing was in place.
The PM’s officials worked long hours, often late into the night as the Government struggled to get to grips with the pandemic.
However, sources claimed the No 10 operation had tried to justify the gatherings because the attendees all worked in the same building.
One said: “It’s difficult to arbitrate because there’s huge amounts of work going on - from time to time until the early hours of the morning.
“They generally observed the rules, it’s just these events happened occasionally that pushed it.”
But another source suggested that ‘letting off steam’ was not an excuse for the scale of gatherings that took place during the run-up to last Christmas.
“Tell that to doctors and nurses and social care workers," they said.