Downing Street has apologised directly to the Queen for the raucous party held in No10 on the eve of the Duke of Edinburgh's funeral but has not released details of what exactly was said.
Boris Johnson's government is coming under increasing pressure about the culture at Downing Street after a series of rule-breaking parties were reported by the media.
Several senior members of the Conservatives have called for Johnson to resign and there is speculation he could soon face a vote of no confidence.
James Slack, Johnson's former director of communications, has apologised "unreservedly" for the party held to mark his leaving Downing Street.
Downing Street has apologised to the Queen after it was revealed a party was held in Number 10 on the eve of the Duke of Edinburgh's funeral.
The Telegraph revealed on Thursday night that as Her Majesty prepared to say goodbye to her husband of 70 years, staff in Downing Street held a raucous leaving party that 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.
At the time England was under strict rules to stop the spread of COVID, and Prince Philip's funeral was limited to only 30 people.
One of the defining images of the pandemic became the image of the Queen sat on her own, having to be distanced from her own family as she grieved the loss of her husband.
A spokesperson for the PM said: "It’s deeply regrettable that this took place at a time of national mourning and number 10 has apologised to the palace.”
Buckingham Palace has declined to respond to the announcement of the apology.
Leader of the opposition Sir Keir Starmer reiterated his calls for Johnson's resignation following Downing Street's admission of an apology over the party.
“This shows just how seriously Boris Johnson has degraded the office of Prime Minister,” Sir Keir said.
Liberal Democrat leader Sir Ed Davey urged Johnson to personally apologise to the Queen and resign over the parties.
“Boris Johnson should apologise personally to the Queen for the offence he’s caused her and millions around the country mourning for loved ones,” he said.
Senior civil servant Sue Gray is including the party on 16 April as part of her investigation into widespread allegations of parties in Downing Street during lockdown.
Johnson's former director of communications, James Slack, earlier apologised for the party held to mark his leaving Downing Street.
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.
The news also comes amid a wider conversation of the culture within Downing Street, after 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.
The prime minister has been facing increasing calls to resign, including from within senior members of his own party.
He is also facing plummeting ratings with voters, and a recent YouGov poll has put his favourability at an all time low - with 72% of the public saying they have an unfavourable opinion of the prime minister.
More than half of Tory voters (52%) also say they have an unfavourable opinion of Johnson, of their leader, casting doubt on how long he can remain in the post.
He is not making public appearances this week after a family member tested positive for COVID on Thursday morning.
There are rumours growing he could face a vote of no confidence in the coming weeks as the party begins to crumble around him.
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.
'Deeply regrettable': The apology explanation from Boris Johnson's spokesperson in full:
Does the prime minister feel he owes an explanation to Queen?
It’s deeply regrettable that this took place at a time of national morning and Number 10 has apologised to the Palace. I was going to say that you’ve heard from the PM this week. He’s recognised Number 10 should be held to the highest standards and taking responsibility for things we did not get right. So, as I said, we have apologised in the past.
Why is it Number 10 apologising the the Palace, not Boris Johnson himself?
The prime minister said earlier misjudgments have been made. And it’s right people apologise as the PM did earlier this week. It remains the case that I can’t [preempt an] inquiry which is ongoing which has been led by Sue Gray. But we acknowledge the significant public anger. It was regrettable this took place at a time of national mourning.
Will the PM apologise to the Queen himself personally?
As I’ve said Number 10 has apologised to the palace. Again, I would obviously not get into any details of the private conversations the PM has with the Queen.
Just getting back to this apology from Number 10 to the palace. What exactly is number 10 apologising for?
Well, as I say, It’s regrettable that this took place at the time of national mourning. And as I say we have we apologised to the Police for that.
Can we have a readout of Number 10's apology to the Palace?
As we said before we [don’t share] individual conversations with the police. But as I’ve set out we have apologised to them.
Is Number 10 apologising to the Palace that something, but they don’t know what, occurred on April 16th?
“As I set out at the start, that the Prime Minister has been clear that misjudgments have been made and it’s right the people apologise as the pm did earlier this week. And as I say, it was deeply regrettable this took place during a period of national mourning which is why we’ve apologised to the Palace but I’m obviously not in a position to be able to get into the any details. Other than that given the Sue Gray review and the fact that it’s ongoing.”