The Labour leader said: “The prime minister doesn’t deny there was a Downing Street Christmas party last year ... He says no rules were broken. Both of those things can’t be true. He’s taking the British public for fools.”
Sir Keir quoted from the “clear” Covid rules in place when London was under tier 3 restrictions, which stated: “You must not have a work Christmas lunch or party.”
He added: “Does the prime minister really believe that while the country was banned from seeing loved ones at Christmas last year, it was fine for him and his friend to throw a boozy party at Downing Street?”
The Daily Mirror reported that Mr Johnson gave a speech at a packed leaving do for a senior aide last November when the country was in the midst of the second lockdown.
The newspaper said members of his No 10 team then held their own festive party in the days before Christmas while London was under tier 3 restrictions.
In each case there was reportedly 40 or 50 people crammed “cheek by jowl” into a medium-sized room. “It was a Covid nightmare,” one source claimed, while another said there were “many social gatherings” at No 10 at the height of the second lockdown.
One partygoer at the 18 December event later told the BBC there were “several dozen” people there, that food and drink were served, games played – and then it went on past midnight.
Grilled over the Downing Street party at the start of PMQs on Wednesday, Mr Johnson deflected and urged Sir Keir to follow current guidance when he holds his own party on 15 December “to which he’s unaccountably failed to invite the deputy leader [Angela Rayner]”.
The Labour leader responded: “Nice try, but that won’t work,” before going on to question the refusal of some Conservative MPs to wear masks in the Commons.
“As for following the rules, prime minister – it might be worth looking behind you when it comes to the question of masks,” said Sir Keir. “As ever, one rule for them, one rule for everybody else.”
It was reported that the official No 10 staff party was cancelled but that the leaving do still took place on 27 November, while an unofficial Christmas party was held on 18 December. Mr Johnson did not attend the latter event, it was claimed.
A Downing Street source did not deny that parties had taken place, telling reporters only: “We don’t recognise this account. At all stages the rules have been followed.”
Leading barrister Adam Wagner, an expert on Covid restrictions, said rules were “probably broken” at the 18 December gathering if 40 to 50 people did attend.
“At the time (Tier 3), you could only have gatherings over 30 indoors if they were a ‘permitted organised gathering’, but that would require households not mingling, or if ‘reasonably necessary for work’,” he tweeted.
“But a Christmas party was very unlikely to be ‘reasonably necessary for work’ … I think that purely social gatherings which weren’t e.g. combined with work meetings – like a Christmas party – weren’t ‘reasonably necessary’.”
Earlier on Wednesday, health secretary Sajid Javid said “all rules would have been followed” if there had been parties in the run-up to last Christmas.
Questioned on LBC, Mr Javid said: “I don’t know who attended these parties – but I don’t even think there were parties, that I’m aware of.”
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies