One former Met protection officer, who has worked in Downing Street, said he thought it “inconceivable” that those on duty on the night of the alleged party would not have had an inkling that something was going on inside No 10.

He said: “Your main priority as a police officer is to enforce the law whether you are in Downing Street or in any other street in the land. If you believe that an offence has taken place then you are bound to intervene or report the matter according to your codes of conduct.”

But Ken Marsh, chairman of the Metropolitan Police Federation, dismissed the suggestion that those on duty would have been aware of any party happening.

He said; “People were not coming into Downing Street in hats, pulling party poppers and singing. They were members of staff coming into work. Nobody was coming out of the building staggering around

‘It is quite simply absurd to have this sort of criticism thrown at my officers’

“The doors and windows of Downing Street are reinforced and soundproof so those outside would not hear a thing that was going on inside the building.

“It is quite simply absurd to have this sort of criticism thrown at my officers.”

In the House of Commons on Wednesday, Prime Minister Boris Johnson said he would cooperate with any police investigation should one be launched.

Speaking at Prime Minister’s Question Time, Keir Starmer, the Labour leader said: “Today at Westminster Magistrates’ Court the Crown Prosecution Service is prosecuting over a dozen Covid breaches from last December involving those who hosted parties. They are doing their job in enforcing the law set in Downing Street.

“Will the Prime Minister support the police and the CPS by providing everything the Government knows about parties in Downing Street to the Metropolitan Police?”

Mr Johnson confirmed that he would.