Boris Johnson's former director of communications has apologised "for the anger and hurt caused” by a party held to mark his leaving Downing Street in April 2021.
Two Downing Street parties were held the night before the Duke of Edinburgh’s funeral in April, The Telegraph reported.
James Slack, who now works as the deputy editor-in-chief of The Sun, said: “I wish to apologise unreservedly for the anger and hurt caused. This event should not have happened at the time that it did. I am deeply sorry, and take full responsibility.”
He said he could not comment further as the matter had been referred to Sue Gray’s investigation.
At the time of the party, funerals were limited to 30 people and the Queen was pictured sitting alone at the service to mourn her husband of 70 years.
According to the Telegraph, the raucous party saw a staff member going to the shops with a suitcase to buy alcohol, and a swing used by the PM's toddler son was broken in the garden during the gathering.
The prime minister was not in Number 10 at the time and is believed to have been at Chequers.
Downing Street has not denied the details in the reports, but issued a statement saying Slack gave a "leaving speech" on the date in question.
A spokesperson said: “On this individual’s last day he gave a farewell speech to thank each team for the work they had done, both those who had to be in the office and on a screen for those working from home.”
It is the latest in an increasingly long line of allegations that parties were held inside the walls of Downing Street while the rest of the country was banned from socialising in groups indoors.
On Wednesday, Johnson issued a grovelling apology after he admitted attending a party in the gardens of Downing Street during the height of the first lockdown, when social gatherings were banned under COVID legislation.
He is not making public appearances this week after a family member tested positive for COVID on Thursday morning.
Despite a number Cabinet ministers rallying to defend him, Johnson is facing increasing calls from within his own party to resign as prime minister.
Watch: Number 10 accused of a culture of drinking under Boris Johnson
Tory MP Sir Roger Gale said the parties were “wholly unacceptable”, but added he does not hold the Prime Minister responsible for the events but for overseeing “a culture” of bending the rules.
He told Sky News: “I think the events that took place on that evening (in April 2021) were wholly unacceptable and completely insensitive, and should never have happened.
“That said, I don’t hold the Prime Minister personally responsible, because he was not there, but it does reveal, I think, a culture within Downing Street that obviously stems from the top and should not be permitted.
“It is just another event in a chapter of incidents which should not have happened."
It is thought backbench MPs are mounting a rebellion against their under-fire PM, and rumours of a vote of no confidence are gaining steam.
Gale added: “I do think that minds are now, over this weekend, being focused upon the need to take the necessary action
“I clearly don’t know, and I shouldn’t know, how many of my colleagues have put in letters – I’m not canvassing them or seeking support for what I have done myself – but I believe that there is some momentum which is growing.”
In order for a vote of no confidence to be called, 15% of Tory MPs — in this case 54 of them — must write to the chair of the 1922 Committee saying they have lost confidence in Johnson as their leader.
Five MPs have so far confirmed they have sent their letters in.