This year's 10 Downing Street Christmas party has been cancelled amid growing anger over a gathering that occurred last December when London was under strict Covid restrictions.
But Boris Johnson has declared his full confidence in communications chief Jack Doyle, after it emerged that he had spoken at last year's event.
An inquiry is under way into what happened at the party and who attended.
Labour leader Sir Keir Starmer called the prime minister "unfit for office".
The revelation of Mr Doyle's speech at the Downing Street gathering on 18 December last year - at which he also handed out awards to staff - follows a tumultuous few days for the government, with Labour accusing it of not being honest about parties in lockdown.
The 18 December gathering, involving between 20 and 30 people. took place two days after London had gone into Tier 3 lockdown restrictions, meaning people could not mix indoors with anyone outside their household or support bubble.
No 10 has refused to explain how this complied with the rules in place at the time.
On Wednesday, government spokeswoman
Allegra Stratton resigned after video footage of her joking with colleagues in relation to the 18 December party was revealed by ITV.