BORIS Johnson has insisted “I certainly broke no rules” but said the Whitehall investigation into potentially lockdown-breaking Christmas parties in Number 10 will include his festive quiz.

The Prime Minister is facing allegations that he may have misled Parliament and suggestions he might have personally broken the rules with his participation in the game last winter.

Johnson denied the claims on Monday and confirmed Cabinet Secretary Simon Case’s investigation will include the quiz.

The head of the Civil Service was already investigating claims of a December Christmas party and November staff leaving do at No 10, as well as festive drinks at the Department for Education.

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Downing Street admitted Johnson “briefly” attended the “virtual” quiz, reported to have been held on December 15 last year, after photographic evidence emerged.

An image published by the Sunday Mirror shows the Prime Minister flanked by colleagues, one draped in tinsel and another wearing a Santa hat, in the No 10 library.

The newspaper quoted a source who said many staff were huddled by computers in their Downing Street offices, conferring on questions and drinking alcohol while the quiz was taking place.

Tier 2 restrictions in London on December 15 said there could be no mixing of households indoors, apart from support bubbles, and a maximum of six people outside.

Speaking to broadcasters during a visit to a vaccination clinic near Paddington in west London, the Prime Minister said: “I can tell you that I certainly broke no rules – the whole thing will be looked into by the Cabinet Secretary, and what I’m focused on, frankly, is the vaccine rollout.”

Pressed if that means Case’s investigation will include the quiz, Johnson replied: “He’s looking at all these things. Is that the thing with the Zoom call? Yeah.”

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He said the results would come back “as soon as we reasonably can” as he stressed the need for booster jabs to combat the threat of the Omicron variant of Covid-19.

Labour said the Prime Minister “might have misled” MPs after he told the Commons he had been given assurances that social distancing regulations were not broken by No 10 last year.

Sir Keir Starmer said it is “very hard” to see how the Tier 2 rules could have been adhered to in the quiz, but stopped short of calling on Johnson to resign.

Official guidance set out there should be no work lunches or parties “where that is a primarily social activity” and they were not exempted for “work purposes”.