A video obtained by ITV News shows senior Downing Street staff joking about a Christmas party in No 10 last year.
The clip from a mock press conference features the then prime minister’s press secretary Allegra Stratton fielding practice questions.
ITV News said the filming took place on 22 December, four days after the party was held.
No 10 said in response to the clip: “There was no Christmas party. Covid rules have been followed at all times.”