LONDON — Downing Street has apologized to Buckingham Palace for two staff parties in No. 10 the night before Prince Philip's funeral, BBC reported.

The gatherings, first reported by The Telegraph, took place on 16 April 2021 and went on until the early hours.

The PM's spokesman said it was "deeply regrettable that this took place at a time of national mourning".

Boris Johnson was not at either party - but he faces questions over alleged Covid rule-breaking at No. 10.

The latest party revelations led to a backlash from opposition parties, who contrasted the behavior of No. 10 staff with pictures of the Queen sitting alone at the Duke of Edinburgh's funeral, due to Covid restrictions.

The two staff get-togethers, on 16 April last year, took place at a time when Covid restrictions banned indoor socializing.

They have been added to the list of gatherings in government buildings being investigated by senior civil servant Sue Gray.

After the apology, Labour leader Sir Keir Starmer said: "This shows just how seriously Boris Johnson has degraded the office of prime minister.

"The Conservatives have let Britain down. An apology isn't the only thing the prime minister should be offering the palace today.

"Boris Johnson should do the decent thing and resign."

It is understood that the apology to the Palace was made by government officials.

Asked why No. 10 had apologized rather than Boris Johnson himself, his spokesman told reporters: "Well, again, the prime minister said earlier misjudgments have been made and it's right people apologize, as the PM did earlier this week."

The spokesman says he could not prejudge Sue Gray's inquiry, but added: "We acknowledge the significant public anger, it was regrettable this took place a time of national mourning."

Liberal Democrat leader Sir Ed Davey called on Johnson to apologize personally to the Queen "for the offense he's caused her and millions around the country mourning for loved ones".

The two parties last April involved around 30 people in total, and are reported to have converged at some point in the Downing Street garden, where they continued past midnight.

They were both leaving parties: one for the PM's then director of communications, James Slack, and the other for one of the PM's personal photographers.

Slack, who is now deputy editor of The Sun newspaper, has apologized for the "anger and hurt" caused by the party, and acknowledged it "should not have happened at the time that it did".

At the time, England was under "step two" restrictions that stipulated people could not socialize indoors, except with those from their household or support bubble.

People could socialize outdoors in groups of up to six people or two households.