Boris Johnson's most senior communications adviser addressed staff and handed out awards on the night of the alleged Downing Street party last year during a time of strict COVID restrictions, it is understood.
Jack Doyle, the director of communications in Number 10, thanked staff working there "like he does every week".
Downing Street Christmas parties: How many events are now under investigation and when were they?
The political adviser in overall charge of Mr Johnson's communications also gave out "thank you awards" on the night of 18 December, Sky News understands.
ITV News was first to report Mr Doyle was present on the evening in question.
Mr Doyle has overseen the communications strategy which has seen Number 10 deny for a week that there was a party, after the Daily Mirror first revealed details.
According to sources who have spoken to Sky News, the event on 18 December was a party which took place with around 40 people in attendance.
Following leaked footage of Number 10 aides laughing about an event, Mr Johnson has tasked the Cabinet Secretary Simon Case with investigating what happened and whether they were telling the truth.
Investigation 'exposed as the sham it is'
This latest development puts more pressure on the PM over the party, a saga that has provoked a backlash and caused disquiet within his party.
Labour leader Sir Keir Starmer tweeted: "Boris Johnson is unfit to lead our country."
And, speaking to the Daily Telegraph, Sir Keir said Conservative MPs should act and force out Mr Johnson before the next election, currently set for 2024.
"Are they prepared to endure the next two years of increased degradation of themselves and their party, being put out to defend the indefensible and bringing themselves and their party into further disrepute?
"Because this isn't going to change - he's unfit for office, it isn't going to change. Or are they going to do something about it?"
Labour's deputy leader Angela Rayner said the Cabinet Office investigation had already "been exposed as the sham it is".
She said: "The investigation has only just published its terms of reference and we are already seeing more details from the media than the Cabinet Office about the parties."
Speaking at PMQs on Wednesday, the PM apologised and said he was "furious" at the footage, but told MPs he has been "repeatedly assured" no such gathering took place.
Allegra Stratton, one of the advisers who was seen in the video joking about a Christmas party, announced her resignation later that day.
The footage, obtained by ITV News, is reported to be of a rehearsal for a TV media briefing from 22 December last year - four days after the alleged Christmas party took place.
Senior Number 10 aides are heard jokingly referring to a "business meeting" and a "cheese and wine" event.
London had been put into Tier 3 restrictions on 16 December 2020, preventing mixing indoors between households.
What events are being looked into?
The cabinet secretary's investigation will look into events on 18 December, as well as gatherings on 27 November and 10 December.
According to reports, the former was a leaving party for a member of staff in Downing Street at which the PM made a speech. This was during the second national lockdown.
The latter was a party held at the Department for Education which was attended by then-education secretary Gavin Williamson.
The event was at a time when London was in Tier 2, with indoor mixing banned.
"Credible allegations relating to other gatherings" may also be investigated, according to the terms of reference of Mr Case's investigation that were published on Thursday.
According to Dominic Cummings, Mr Johnson's former chief adviser, a party took place in the Downing Street flat on 13 November on the day he left his Number 10 role. Downing Street denies this.
A Conservative spokesperson has confirmed to Sky News that, on 14 December, an "unauthorised social gathering" was held at Conservative Campaign Headquarters, organised by the campaign of the party's London mayoral candidate Shaun Bailey.
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2021-12-10 07:10:44Z
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