The health secretary says other gatherings held last year could be included in an official investigation.
An investigation into a Christmas party in Downing Street last year could be widened to include other gatherings.
Health Secretary Sajid Javid said top civil servant Simon Case, who is looking into an 18 December party, was “not fixated” on a single date.
Get-togethers are also reported to have taken place on 13 and 27 November, when a Covid lockdown was in place.
The PM announced an inquiry into the 18 December party on Wednesday after a video emerged of staff joking about it.
The government has continued to insist that no party took place on 18 December, at which time London was under strict Covid rules, with people banned from meeting indoors or in private gardens.
But, under pressure from Labour and amid criticism from some of his own MPs, the prime minister announced on Wednesday that Mr Case would try to establish the facts about what happened.
He said anyone found to have broken Covid rules would face disciplinary action.
Mr Javid told BBC Radio 4’s Today programme he had received assurances from senior figures that no party had taken place on 18 December, but he added: “[Mr Case is] not fixated on a particular date. I think that’s important, and that they establish the facts.”
Reports of Downing Street parties have caused a political and public backlash.
Government spokeswoman Allegra Stratton resigned on Wednesday after a video filmed on 22 December last year – four days after the 18 December party – showed her joking with a colleague about it.
In a tearful resignation statement, she said the video, obtained by ITV News, she said she was “truly sorry”.
Mr Javid said he had been “upset” and “angered” by the video, adding: “I think there is a need to have an investigation because I think there’s enough doubt that’s been thrown on this by some of the reports and by looking at that video.”
Ask why Ms Stratton had resigned, despite there being no suggestion she had attended the party, he said: “Look, I wouldn’t know, I haven’t spoken to her about it.
“Perhaps it was because she was very embarrassed by the video and what happened and the way things looked. It may well be something like that.”
The Metropolitan Police announced on Wednesday night that it was not investigating allegations of Covid rule breaking at the 18 December party due to “an absence of evidence”, but Labour said this was “simply implausible”.
Labour deputy leader Angela Rayner said the 18 December party did not look like a “one-off incident”.
She told BBC Breakfast: “There is a number of allegations around parties at the flat at No 10, parties in No 10, parties in other departments.
“And this is devastating news for people that did the right thing last Christmas, who lost loved ones, who wasn’t able to visit them before they died.
“And quite rightly people are very angry about this and the government are not above the law, and they should be held accountable for their actions.”
The events surround the Downing Street party on 18 December have angered many including some Conservatives.
Scottish Conservative leader Douglas Ross has said Mr Johnson should quit if he was found to have misled Parliament.
13 November 2020: Sources have told the BBC there were impromptu drinks to mark the exit of the former director of communications at No 10, Lee Cain – but it was staff having drinks at their desks and was over by 20:30.
13 November 2020: Also the date Dominic Cummings left as chief adviser to the PM. Sources told the BBC that several Downing Street staff members attended a gathering with Carrie Johnson in the flat where the prime minister and his wife live above No 11 after exits. A source said music was blaring and could be heard elsewhere in the building. But others said to be at the party denied it took place, as did a spokeswoman for Mrs Johnson.
27 November 2020: Another No 10 aide, Cleo Watson, left Downing Street marked by an event. Again, sources said it was not formally organised, but people were having drinks and Mr Johnson made a speech.
1 December 2020: The Conservatives have confirmed reports that there was an “unauthorised social gathering” in the basement of their party’s building, held by the team of the London mayoral candidate at the time, Shaun Bailey. It was described as “raucous”. Four Tory staff members have been disciplined.
December 10 2020: The Department for Education has confirmed it had a gathering in the office to thank staff for their work during the pandemic. Drinks and snacks were brought by those who attended and no outside guests or support staff were invited.
18 December 2020: The now infamous Downing Street Christmas party took place on this date, as first reported by the Mirror. A source told the BBC there was food, drinks and games at the gathering that went on past midnight.
Another December party: We are still trying to pin down the date of this one, but multiple sources have told the BBC there was a Christmas quiz for No 10 staff in the Cabinet Office, with invites sent out in advance via email, telling people to form teams of six. Downing Street have said it was a “virtual gathering” but while some joined in that say, sources said there were groups in the room sat in their teams.