Boris Johnson is believed to have attended at least six gatherings being probed by a police inquiry into lockdown parties in Whitehall and Downing Street.
Scotland Yard is investigating 12 rule-breaking events after U-turning in January on its initial refusal to probe Partygate allegations.
The force confirmed on Tuesday that 20 fixed penalty notices are being referred to the ACRO Criminal Records Office as part of the first wave of fines.
