According to the Metropolitan Police, investigators will begin to refer the notices to the ACRO Criminal Records Office, which would be responsible for issuing the fines.
And more fines are expected as the probe continues.
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.
“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 [force].
“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.”
On the day of the gathering, in May 2020, Northumbria Police received more than 200 reports of possible coronavirus-related offences.
The Met would not confirm how many individuals will receive fines, or their identities, in line with guidance from the College of Policing.
Officials in Downing Street have said they will confirm if the Prime Minister is fined.