Police are reviewing their initial decision not to investigate a Christmas quiz in Number 10, held at a time of strict COVID rules, after a picture of Boris Johnson and a bottle of alcohol emerged.

Scotland Yard said they would rethink their assessment of the event following the publication of an image of the prime minister next to alcohol, crisps, a person wearing tinsel and another wearing a Santa hat.

At the time of the event, on 15 December 2020, London was under Tier 2 coronavirus restrictions.

This banned any social mixing between two or more people from different households.

Scotland Yard said in a statement: “The Metropolitan Police service previously assessed this event and determined that on the basis of the evidence available at that time, it did not meet the threshold for criminal investigation.

“That assessment is now being reviewed.”

Although the 15 December event was previously not among the allegations of COVID rule-breaking in Number 10 being investigated by the Met Police, it has formed part of an inquiry by senior civil servant Sue Gray.

She has yet to publish her full findings due to an ongoing Met Police probe into 12 other alleged lockdown-busting gatherings in Downing Street.

Ms Gray has handed more than 300 images and more than 500 pages of information to Scotland Yard.

Now the Met Police are reviewing the 15 December event, it has led to the possibility of a 13th gathering being added to their investigation.

Earlier on Wednesday, as Mr Johnson was speaking at Prime Minister’s Questions in the House of Commons, the Daily Mirror published the fresh image of the 15 December event.

Labour MP Fabian Hamilton challenged Mr Johnson about the photo of him “surrounded by alcohol, food and people wearing tinsel”.

He asked whether the prime minister would “be referring that party to the police, as it is not one of those already being investigated”.

The prime minister told Mr Hamilton he was “completely in error” and, challneged again later, added that the 15 December event “already has been submitted for investigation”.