Here is a look at what happened and who said what about the event which took place during a coronavirus lockdown.
London is placed under Tier 3 coronavirus restrictions, the highest level of curbs on freedoms at the time, with a ban on people from different households mixing indoors.
Staff in Downing Street are believed to have held a Christmas party, with reports that dozens of people attended the event, some wearing festive jumpers and exchanging Secret Santa presents.
The Daily Mirror reveals the Christmas party took place, reporting that “officials knocked back glasses of wine during a Christmas quiz and a Secret Santa while the rest of the country was forced to stay at home”.
At Prime Minister’s Questions, Mr Johnson said “all guidance was followed completely”.
Labour leader Sir Keir Starmer said: “Does the Prime Minister really expect the country to believe that whilst people were banned from seeing their loved ones at Christmas this year it was fine for him and his friends to throw a boozy party in Downing Street?”
Business Minister George Freeman says: “I can absolutely assure you that No 10 staff followed the guidance,” adding: “I can’t get drawn into who was or wasn’t in the room and who was drinking which cocktail. You’ll understand I wasn’t there.”
Tory chairman Oliver Dowden says: “My focus has not been on having conversations about what may or may not have happened over a year ago in Downing Street. I have, however, been assured by what the Prime Minister has said, which is that the rules at all times were obeyed in Downing Street.”
The Metropolitan Police says it is considering the correspondence it had received in relation to the Christmas party and an earlier gathering in November 2020 which the Prime Minister reportedly attended.
Deputy Prime Minister Dominic Raab says “if there was a formal party held, of course that is something that is clearly contrary to the guidance”, but insisted he did not know the truth of the reports based on “unsubstantiated claims all on the basis of anonymous sources”.
Policing Minister Kit Malthouse says: “I asked the question: ‘Were all the regulations complied with?’ I was reassured they were, I have to take that at face value. That’s absolutely what I’m sure is the case; it’s for others if they want to decide to take it further.”
Mr Johnson says: “I am satisfied myself that the guidelines were followed at all times.”
Downing Street responds: “There was no Christmas party. Covid rules have been followed at all times.”
The Metropolitan Police says the footage “will form part of our considerations”.
Health Secretary Sajid Javid is pulled from a scheduled round of broadcast interviews.
Mr Johnson faces Prime Minister’s questions in the Commons.