Downing Street has apologised to Buckingham Palace for two staff parties in No 10 the night before Prince Philip's funeral.

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 behaviour 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 socialising.

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 apologised rather than Boris Johnson himself, his spokesman told reporters: "Well, again, the prime minister said earlier misjudgements have been made and it's right people apologise, 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 Mr Johnson to apologise personally to the Queen "for the offence he's caused her and millions around the country mourning for loved ones".

Earlier, Foreign Secretary Liz Truss said she was "very concerned" about the latest revelations, and understood that "people across the country are angry".

She also urged people to wait for Ms Gray's inquiry, but added: "we are very clear that there were real mistakes made".