The Metropolitan Police said on Tuesday that investigators will begin to refer the notices to the ACRO Criminal Records Office, which would be responsible for issuing the fines.

It is expected that further fines could be issued as officers continue to go through the evidence gathered.

The force said: “The investigation into allegations of breaches of Covid-19 regulations in Whitehall and Downing Street has now progressed to the point where the first referrals for fixed penalty notices (FPN) will be made to ACRO Criminal Records Office.

The first Partygate fines have been confirmed by police.

“We will today initially begin to refer 20 fixed penalty notices to be issued for breaches of Covid-19 regulations. The ACRO Criminal Records Office will then be responsible for issuing the FPNs to the individual following the referrals from the MPS.

“We are making every effort to progress this investigation at speed and have completed a number of assessments. However, due to the significant amount of investigative material that remains to be assessed, further referrals may be made to ACRO if the evidential threshold is made.”

The Met would not confirm how many individuals will receive fines, or their identities.

It said: “As it has for all fixed penalty notices issued during the pandemic, the MPS will follow the College of Policing Approved Professional Practice for Media Relations which states that “Identities of people dealt with by cautions, speeding fines and other fixed penalties – out-of-court disposals – should not be released or confirmed.”

“We will not confirm the number of referrals from each individual event subject to our investigation as providing a breakdown at this point may lead to identification of the individuals.”

However, Downing Street will confirm if the Prime Minister is issued with an FPN, but it is not expected to confirm the identities of more junior members of staff who are hit with fines.

Labour’s deputy leader Angela Rayner said the partygate saga had been a “slap in the face” for the public after fixed penalty notices were issued by the Metropolitan Police.

Ms Rayner said: “After over two months of police time, 12 parties investigated and over a hundred people questioned under caution, Boris Johnson’s Downing Street has been found guilty of breaking the law.

“The culture is set from the very top. The buck stops with the Prime Minister, who spent months lying to the British public, which is why he has got to go.

“It is disgraceful that while the rest of the country followed their rules, Boris Johnson’s Government acted like they did not apply to them.

“This has been a slap in the face of the millions of people who made huge sacrifices.“

Liberal Democrat Leader Sir Ed Davey said: “If Boris Johnson thinks he can get away with partygate by paying expensive lawyers and throwing junior staff to the wolves, he is wrong.

“We all know who is responsible. The Prime Minister must resign, or Conservative MPs must sack him.”

More than 100 police questionnaires had been sent out to people at the gatherings.

These events included a “bring your own booze” gathering, details of which were emailed to staff at No 10 by the Prime Minister’s principal private secretary Martin Reynolds in May 2020, and a surprise get-together for Mr Johnson’s birthday in June 2020.

Mr Johnson previously admitted he was at the “socially-distanced drinks” organised by Mr Reynolds for 25 minutes – claiming he believed it was a work event – while Downing Street said staff “gathered briefly” in the Cabinet Room to mark the Prime Minister’s 56th birthday.

The police are also investigating a party in Mr Johnson’s Downing Street flat on November 13 2020 – reportedly hosted by his wife Carrie on the night of the Prime Minister’s controversial aide Dominic Cummings’ acrimonious exit from No 10.

In January, civil servant Ms Gray published a report into the allegations of the parties, which said there were “failures of leadership and judgment” in parts of No 10 and the Cabinet Office while England was under coronavirus restrictions in 2020 and 2021.

The initial publication contained limited detail due to the police investigation but a fuller report is expected once the Met’s inquiry concludes.

First 20 fines confirmed by Met Police over Partygate - with more to come