POLICE are not opening an investigation into allegations Downing Street staff broke coronavirus rules with a Christmas party last year, as Boris Johnson apologised and a senior aide was forced to quit over the scandal.

Scotland Yard said officers will not “commence an investigation at this time” in line with its “policy not to investigate retrospective breaches” of coronavirus rules despite reviewing the allegations and leaked footage showing senior No 10 staff joking about a party.

But the Metropolitan Police was open to considering any further evidence unearthed in an internal investigation the Prime Minister was forced to task Cabinet Secretary Simon Case with undertaking as he claimed to be “furious” about the video.

Amid mounting public anger Allegra Stratton, who was the Prime Minister’s spokeswoman, resigned as a Government adviser after video emerged of her and other aides “seeming to make light of lockdown measures” just days after the gathering in No 10.

A Met statement acknowledged it had received “a significant amount of correspondence” relating to the alleged breaches in the run up to Christmas last year but said they do not “provide evidence of a breach” of Covid rules.

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“Based on the absence of evidence and in line with our policy not to investigate retrospective breaches of such regulations, the Met will not commence an investigation at this time,” it added.

“The Met has had discussions with the Cabinet Office in relation to the investigation by the Cabinet Secretary. If any evidence is found as a result of that investigation, it will be passed to the Met for further consideration.”

Johnson has repeatedly insisted that rules were followed in Downing Street since the claims first emerged about the December 18 party.

However, at Prime Minister’s Questions, he told the Commons he based that position on assurances from junior staff as he offered an apology.

He asked Case “to establish all the facts and to report back as soon as possible – and it goes without saying that if those rules were broken then there will be disciplinary action for all those involved”.

Johnson said: “I understand and share the anger up and down the country at seeing No 10 staff seeming to make light of lockdown measures, and I can understand how infuriating it must be to think that people who have been setting the rules have not been following the rules because I was also furious to see that clip.

“I apologise unreservedly for the offence that it has caused up and down the country, and I apologise for the impression that it gives.

“But I repeat that I have been repeatedly assured since these allegations emerged that there was no party and that no Covid rules were broken, and that is what I have been repeatedly assured.”

At a hastily-arranged Downing Street press conference, Johnson was forced to deny allegations, including from senior Conservative William Wragg, that his announcement of further coronavirus restrictions was a “diversionary tactic” from the scandal.

The Prime Minister also appeared to concede that the Cabinet Secretary would be able to go further than just reviewing the events of December 18 and “look at other things”, with other alleged gatherings in Downing Street over the festive period last year.

Johnson praised Stratton as a “fine colleague” as he accepted her resignation.

“Allegra Stratton has resigned and I wanted to pay tribute to her because she has been, in spite of what everybody has seen, and again, I make no excuses for the frivolity with which the subject was handled in that rehearsal that people saw in that clip,” the Prime Minister said.

In a tearful statement outside her home, Stratton apologised for her appearance in footage recorded just days after the alleged party.

She had been taking part in a mock press conference in preparation for the planned White House-style televised briefings she would front – a project which was ultimately abandoned.

​READ MORE: Allegra Stratton resigns from role in Boris Johnson's team

In the footage obtained by ITV News, Stratton and adviser Ed Oldfield, along with other aides, were filmed joking about a “fictional” Downing Street party.

A laughing Stratton said: “This fictional party was a business meeting … and it was not socially distanced.”

Her appearance in the briefing room was in stark contrast to her emotional statement on Wednesday, where she told reporters: “My remarks seemed to make light of the rules, rules that people were doing everything to obey.

“That was never my intention. I will regret those remarks for the rest of my days and I offer my profound apologies to all of you at home for them.”

Stratton, who had been working as Johnson’s spokeswoman for the COP26 climate summit, said she understood people’s “anger and frustration”.

“To all of you who lost loved ones, who endured intolerable loneliness and who struggled with your businesses, I am truly sorry and this afternoon I am offering my resignation to the Prime Minister.”

The Prime Minister’s decision to launch an investigation followed a week of official denials that the party took place when London was under Tier 3 restrictions – despite reports staff drank alcohol and exchanged Secret Santa gifts.

Downing Street’s official line has now shifted with the announcement of the Case inquiry, with the Prime Minister’s press secretary declining to repeat the statement that “there was no party”.

She said “it wouldn’t be right to comment further” while Case was investigating.

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Labour leader Keir Starmer said the Prime Minister’s apology “raises more questions than answers” as he had been “caught red-handed”.

“Millions of people now think the Prime Minister was taking them for fools, that they were lied to. They are right aren’t they?” he added.

In response to questioning from Sir Keir, the Prime Minister agreed that any evidence uncovered by the Cabinet Secretary about parties in Downing Street would be handed over to police.

The emergence of the footage of Stratton’s mock press conference fuelled anger on the Tory benches about Johnson’s No 10 operation.

Scottish Tory leader Douglas Ross said Johnson should quit if he was found to have misled Parliament.

He told Sky News: “If he knew there was a party, if he knew it took place, then he cannot come to the House of Commons and say there was no party.”