An insider at No10 said that officials, also known as custodians sent an email reminder around the building, while another source claimed they were forced to visit the building later to speak with people directly.
Sources have revealed that Downing Street security guards had to warn staff not to hold social gatherings while they were locked down.
One insider at No 10 claimed that officials, also known as custodians, sent an email reminding the building about the incident in the summer 2020.
It was the culmination of a number of gatherings that included Boris Johnson's birthday party in Cabinet room, for which he was fined. This all began when the country emerged from its first lockdown.
Mirror was told by another source that custodians had to visit the building later to talk to people and asked them to end events by 9 p.m.
The incident occurred after an insider revealed to BBC Panorama that one of the custodians was ridiculed for trying to stop a party from going ahead.
"I can recall when the custodian tried stopping it all, and he was shaking his head in that party, being like, ‘This shouldn’t be happening'," they said.
People made fun of him because it was a party that was taking place and shouldn't be taking place.
"How could it have happened, while the rest of the country was under strict lockdown?"
It is published ahead of Sue Gray's report on lockdown parties.
It will likely be damning about party culture that was prevalent at the heart government while the rest of country was adhering to strict lockdown rules.
Expect the report to name Johnson and include a damning verdict.
This comes after it was claimed that Boris Johnson had suggested Sue Gray drop the Partygate report at a secretive meeting.
After No10 officials suggested talks, the Prime Minister, who is Whitehall's boss, met with her this month.
No10 has refused to release minutes. Boris Johnson, Sky News and the Times reported that she asked if it was worth publishing her final verdict regarding lockdown parties following a police investigation.
