The first Partygate fines handed out by police relate to a leaving do for a Cabinet Office official in June 2020, according to reports.
Staff who attended the bash are understood to have received £50 fixed penalty notices by email.
The Metropolitan Police confirmed on Tuesday that they have referred an initial tranche of 20 Partygate cases for fixed penalties.
But police refused to reveal who was being fined or give details of the breaches of coronavirus laws involved.
But ITV political editor Robert Peston today said that at least some of the fines stem from an event at the Cabinet Office on 18 June 2020, believed to have been held to mark the departure of Downing Street official Hannah Young to take up the role of deputy consul general in New York.
There was no immediate response from Downing Street, which has said it will not confirm the identity of anyone fined as a result of the Operation Hillman inquiry, with the exception of Boris Johnson or civil service head Simon Case.
The Metropolitan Police are investigating 12 events in Downing Street and Whitehall in which laws imposed to prevent the spread of Covid-19 are alleged to have been breached in 2020 and 2021.
Fines issued so far are thought to relate to cases where the breach was not disputed. Having taken evidence in questionnaires from more than 100 ministers, officials and advisers - including Mr Johnson and chancellor Rishi Sunak - officers are now conducting interviews with some of those involved.
The prime minister himself has not yet been called for interview. He has refused to acknowledge that the fines already issued constitute proof of law-breaking at No 10 under his watch, insisting that he will not comment until the inquiry concludes.
