The Metropolitan Police is reopening an investigation into breaches of Covid regulations at a Christmas party at Conservative Party HQ.
A video of the gathering, where aides were invited to “jingle and mingle”, was published by the Sunday Mirror.
Police say they will not investigate alleged gatherings at the prime minister’s country home, Chequers, when Boris Johnson was PM.
But they are now investigating an event in Parliament on 8 December 2020.
According to the Guido Fawkes website, this event involved Conservative backbencher Sir Bernard Jenkin.
Sir Bernard sits on the Commons Privileges Committee, which last month published a highly critical report about Mr Johnson.
Sir Bernard told the BBC it was not appropriate to comment on an ongoing investigation.
Separately, Conservative MP Virginia Crosbie issued an apology for attending the event while Covid restrictions were in place.
The Ynys Mon MP confirmed the event took place but said she had not sent out any invitations.
The Met police investigated the December 2020 party at Tory HQ last year, after a picture emerged showing former London mayoral candidate Shaun Bailey and Tory aides raising glasses besides buffet food, when indoor socialising was banned.
In November, the Met said they were taking no further action against Mr Bailey or the others pictured.
They have now said they are reopening their inquiry, as the video published by The Mirror had not previously been provided to officers.
An invitation to the event seen by the BBC invited people to a “jingle and mingle” party.
Mr Bailey said he apologised “unreservedly” for the event, which he said “turned into something” after he had left.
He claimed he was “very upset about the video” as he had “never seen it before”.