A number of parties were held in Downing Street in the run-up to Christmas last year while indoor mixing was banned in London under COVID restrictions, Sky News understands.
Following reports that a large party was held in late December, it has also emerged that Number 10 staff gathered after work and drank alcohol to wind down, despite rules stating that mixing between household bubbles was banned.
Labour deputy leader Angela Rayner has now written to Cabinet Secretary Simon Case, the most senior civil servant, to ask whether he will investigate what happened, or refer the matter to police.
On 18 December, 40 people attended a bash in Downing Street, where staff drank, chatted and celebrated late into the night, according to a report in The Mirror newspaper.
Sky News understands the individuals at this party let their hair down with games, food and drink.
It has been reported as a Christmas party, but one government aide said it was convened to say goodbye to a colleague working in Downing Street who was moving to a new role elsewhere.
On 16 December, two days before the large Downing Street bash allegedly took place, London moved into Tier 3 restrictions, where all indoor mixing was banned unless individuals were in household bubbles.
Downing Street has insisted that no rules were broken during the period.
When pressed on the gatherings staff held throughout the period a Number 10 spokesman said: “COVID rules have been followed at all times.”
On Tuesday, Downing Street was forced to deny claims that Boris Johnson broke coronavirus rules with parties at Number 10 last Christmas after the Mirror newspaper claimed the PM made a speech at a leaving do on 27 November – when the country was in the second lockdown.
The PM’s spokesman on Wednesday reiterated at a regular briefing with journalists that “at all stages the rules have been followed”.
The original story claimed Mr Johnson did not attend the event in December held by members of his top team.
A spokeswoman for the PM’s wife Carrie Johnson denied she hosted the bash or held any parties at the couple’s flat while restrictions were in place.
“This is total nonsense. Mrs Johnson has followed coronavirus rules at all times and it is categorically untrue to suggest otherwise,” she told the Mirror.
Downing Street staff are classified as key workers and have been throughout, with members working long hours to deal with the pandemic.
Labour said the allegations suggest it is “one rule for them, another for everyone else”.
Probing Mr Johnson on the reports at Prime Minister’s Questions on Wednesday, Sir Keir Starmer accused him of holding a “boozy party” in Number 10 last Christmas despite COVID rules that were in place at the time.
The Labour leader said Mr Johnson was “taking the British public for fools”, but the PM said “all guidance was followed completely”.
“The defence seems to be no rules were broken. Well, I’ve got the rules that were in place at the time, prime minister, of this party, they’re very clear,” Sir Keir said.
“You must not have a work Christmas lunch or party. Does the prime minister really expect the country to believe that while people were banned from seeing their loved ones at Christmas last year, it was fine for him and his friends to throw a boozy party in Downing Street?”
Mr Johnson replied: “I’ve said what I’ve said about Number 10 and the events of 12 months ago, but since he asks about what we’re asking the country to do this year which I think is, frankly, a more relevant consideration.”
The Mirror’s original report alleged that around “40 or 50” people were crammed “cheek by jowl” into a room in Number 10 for both events.
Last November, the whole country was plunged into a second national lockdown for four weeks.
As a result, everyone was told to work from home where possible and indoor socialising was banned.
The revelations come after the PM rejected the idea that Christmas parties should be scrapped this year due to the new Omicron variant.
Earlier, top health chief Dr Jenny Harries had warned that people should cut down on socialising during the festive period to curb future COVID infections.
Ms Harries said everyone can do their bit by reducing the number of social contacts they have – and by “not socialising when we don’t particularly need to”.
But the PM rejected Dr Harries’ call, insisting that he had already put in place a package of “balanced and proportionate measures” in response to the threat posed by the new Omicron variant.
Speaking at a Downing Street news briefing, Mr Johnson said: “We don’t want people to cancel such events and we think that, overwhelmingly, the best thing for kids is to be at school, as I have said many times throughout this pandemic.
“What we are doing is trying to take a balanced and proportionate approach to the particular risk that seems to be posed by Omicron – certainly is posed by Omicron – focused, in particular, on measures at the border.”
Identified cases of the new Omicron variant in the UK increased to 32 on Wednesday, with the UK Health Security Agency (UKHSA) confirming that nine more cases have been identified in England and one more in Scotland.
The government said, as of 9am on Wednesday, there had been a further 48,374 lab-confirmed COVID-19 cases in the UK and that a further 171 people had died within 28 days of testing positive.
A total of 50,994,257 first doses of vaccines had been delivered in the UK by 30 November 30, government figures show.