Three young women appeared in court for attending Christmas parties on December 18 last year - the same day as the Downing Street 'bash'.
All three were fined £1,100 each for breaching the government's Health Protection regulations while London was in Tier 3.
Despite the women's convictions, the Met Police have said they are not going to investigate alleged breaches at events in Downing Street on the same day.
Three government events, first revealed by the Mirror, will now be the subject of an inquiry by the Cabinet Office.
Yesterday Boris Johnson finally "apologised unreservedly" over a No10 Christmas party but denied all responsibility.
He continued to claim he was told rules were followed and threw his own staff under the bus.
Mr Johnson said he was "sickened and furious" at a clip of his own staff laughing about a Christmas bash four days after it happened last December, when lockdown rules banned social gatherings.
After a week of stonewalling questions, and No10 claiming there was no party, the PM announced an investigation by the Cabinet Secretary and disciplinary action if the rules were broken.
The investigation will "establish the facts around" at events alleged to have taken place in Downing Street on November 27 and December 18, as well as a gathering at the Department for Education on December 10.
The Evening Standard revealed 26-year-old Ebru Sen, Ami Goto, 23 and Emilia Petruta-Cristea, 24, all appeared at Westminster Magistrates Court.
They are three of many who have been prosecuted for breaking Covid rules last Christmas.
Goto from Marylebone and Sen from Sittingbourne, Kent were each fined £1,100 plus £210 costs for a gathering of two or more people in a flat in Holborn.
Petruta-Cristea was fined and ordered to pay costs of the same amount over a gathering at her home in Wanstead.
The prosecutions have been conducted since September last year in London through a behind-closed-doors Single Justice Procedure.
The Metropolitan Police have said it will not investigate allegations of a party at Downing Street when lockdown rules banned social gatherings.
The force claims this is due to an “absence of evidence” and its policy not to investigate retrospective breaches of coronavirus regulations.
A clip leaked to ITV News of a private ‘mock’ press conference four days after the bash, insinuated it involved a Secret Santa, wine and cheese, a quiz and “40 or 50” people.
Police said the video "does not provide evidence of a breach" of health regulations and therefore the force would not commence an investigation.
