Another government rule-breaking party, held in the Cabinet Office, has been confirmed to have taken place during the Christmas lockdown in 2020.
It was a leaving party held for Kate Josephs, who until December 18 2020, was responsible for drawing up coronavirus restrictions as director-general of the Cabinet Office Covid Taskforce.
Ms Josephs, who is now CEO of Sheffield City Council, issued an apology for holding the drinks event on December 17, telling her Twitter followers she is "truly sorry".
She wrote: "On the evening of 17 December, I gathered with colleagues that were at work that day, with drinks, in our office in the Cabinet Office, to mark my leaving the Civil Service.
"I am truly sorry that I did this and for the anger that people will feel as a result."
"I apologise unreservedly," she added.
On the same day the party was held, the government Twitter account tweeted, telling a follower "you must not have a work Christmas lunch or party".
The event will be looked into by top civil servant Sue Gray, who is running an investigation into at least eight other allegedly rule breaking parties attended by members of the government throughout the pandemic.
This party is understood to have ran separately to another gathering in the Cabinet Office at the same time and 24 hours before a the now-infamous 'cheese and wine' event held in Number 10.
London was under Tier 3 restrictions at the time, meaning social events including parties were banned.
The law clearly stated that “no person may participate in a gathering in the Tier 3 area which consists of two or more people, and takes place in any indoor space”.
The government’s own guidance made clear that people “must not have a work Christmas lunch or party, where that is a primarily social activity”.
Confirmation of the Cabinet Office comes less than 24 hours after two other parties were revealed to have taken place in Downing Street, this time the day before Prince Philip's funeral.
The people at the Downing Street party that night would have been able to see the flags at half-mast around Whitehall, Deputy Political Editor Anushka Asthana reports
Boris Johnson's spokesman said: "It's deeply regrettable that this took place at a time of national mourning and Number 10 has apologised to the Palace."
"You heard from the PM this week, he's recognised No 10 should be held to the highest standards and take responsibility for things we did not get right."
While the latest party does not implicate the prime minister directly, it adds to the idea that there was a culture of rule breaking within government while the rest of the country was forced to endure strict restrictions.
And Tory MPs - the only people with the power to remove the prime minister - are growing angrier with each accusation.
Up to 20 MPs are understood to have submitted letters of no confidence in Mr Johnson, however that is well short of the 54 required to trigger an vote on his leadership.
One Tory told ITV News that staff partying before Prince Philip's funeral would be the "nail in the coffin" for the PM.
Other allegations are now swirling around Westminster about behaviour in Downing Street during Covid restrictions - Anushka Asthana explains
Sheffield City Council leader Terry Fox said the chief executive has discussed with him what happened and apologised face-to-face.
He said: "To be honest I need to express my deep disappointment - people will rightly feel angry and let down. I get that completely.
"After everything that Sheffield has been through during the pandemic, this is news that we did not want to receive.
"Over the last year, Kate's been an asset to our city and she is working tirelessly for Sheffield and it's people.
"Our residents will understandably have questions and concerns, and we await the findings of the investigation."