Boris Johnson has been accused of presiding over a "culture of disregard for the rules" after a picture emerged of him taking part in an online Downing Street quiz last year appearing to be flanked by colleagues.
The image, reported by the Sunday Mirror, appears to show the Prime Minister on a screen sitting in front of a laptop in the No 10 library.
One of his colleagues is draped in tinsel.
Downing Street said the Conservative Party leader had "briefly" taken part in the quiz "virtually" on December 15th last year.
The festive event is said to have taken place only three days before an alleged rule-breaking Christmas party in No 10, which is under investigation by Cabinet Secretary Simon Case.
Deputy Labour party leader Angela Rayner said: "While the rules said that people shouldn’t have Christmas parties at work and Britons across the country were doing the right thing, Boris Johnson was instead happy to preside over a culture of disregard for the rules at the heart of Government.
"Despite repeated denials of parties in Number 10, it now transpires that there were numerous parties, gatherings and the Prime Minister even took part in a festive quiz.
"Boris Johnson really believes it’s one rule for him, another for everyone else.
"He is a man unfit to lead this country."
Official guidance at the time stated: "Although there are exemptions for work purposes, you must not have a work Christmas lunch or party, where that is a primarily social activity and is not otherwise permitted by the rules in your tier."
At the time of the quiz, London was in Tier 2 which said there should be no mixing of households indoors, apart from support bubbles, and maximum of six people outside.
The Sunday Mirror quoted a source who claimed many staff were huddled by computers, conferring on questions and drinking alcohol while the quiz was taking place.
It reported that the PM surprised staff by turning up on screen as quizmaster for one round lasting between 10 and 15 minutes.
A No 10 spokeswoman said: "This was a virtual quiz.
"Downing Street staff were often required to be in the office to work on the pandemic response so those who were in the office for work may have attended virtually from their desks.
"The Prime Minister briefly took part virtually in a quiz to thank staff for their hard work throughout the year."
The quiz reports come as Mr Case, who is also head of the Civil Service, investigates three alleged rule-breaking Government gatherings last winter.
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