Sources have told The Telegraph that Mr Johnson’s case is likely to be among the first to be concluded – raising the prospect that, now he has responded to the questionnaire, he could learn his fate within days.

If he does receive a fine, a series of backbenchers are likely to submit letters of no confidence in a move that would be likely to trigger a vote on his leadership of the Conservative Party. One senior Tory said an announcement that Mr Johnson had received a fine would be a “get off the fence moment” for disaffected MPs.

A Government source acknowledged that a no confidence vote was likely in the event that Mr Johnson received a fine, but insisted he was unlikely to lose if MPs continued to believe that no candidate was ready to succeed him. 

However, the source added that a public challenge by a potential contender such as Rishi Sunak, the Chancellor, could lead to the Prime Minister’s downfall in such a scenario.

If the Met decides Mr Johnson is to be fined, the details will be sent to ACRO, the Criminal Records Office, which will issue the Fixed Penalty Notice.

At the height of the pandemic, when thousands of Covid fines were being issued across the country, it was taking ACRO up to 12 weeks to process and issue a fixed penalty notice. But with all restrictions now lifted, it is thought staff will be able to turn the paperwork around almost immediately.

Detectives are investigating 12 alleged gatherings across eight separate dates between May 20, 2020 and April 16, 2021. But rather than dealing with the cases chronologically, it is understood detectives have focused on the highest profile and most difficult to resolve ones first.

A source with knowledge of the investigation said: “Lots of those contacted by the police are likely to admit the offence and accept the fixed penalty notice. But rather than deal with the low-hanging fruit first, those cases are likely to go to the bottom of the pile, with all the attention going on resolving the complex cases first.”

On Friday, a leaked memo revealed that Downing Street staff accused of attending lockdown-busting parties will be allowed to see Sue Gray’s notes on their interviews before they fill in a police questionnaire.