The email, from Johnson’s principal private secretary Martin Reynolds, invited more than 100 staffers to “socially distanced drinks in the No. 10 garden” on May 20, 2020.
At that time, strict lockdown restrictions were in place in England.
Mixing between households was limited to two people, who could only meet outdoors and at a distance of at least 2 meters (6.5 feet). In workplaces, official guidance stated that in-person meetings should only take place if “absolutely necessary.”
In the email, first published by ITV News on Monday, Reynolds said: “After what has been an incredibly busy period it would be nice to make the most of the lovely weather and have some socially distanced drinks in the No10 garden this evening.”
“Please join us from 6pm and bring your own booze!” the email added.
A source who worked in Downing Street at the time has confirmed the contents of the email independently to CNN.
Pressed on Monday by a journalist to answer whether he and his wife, Carrie Johnson, had attended the party, the prime minister said: “That as you know, is the subject of a proper investigation by Sue Gray.”
Gray, a senior civil servant, has been tasked with investigating the alleged parties. She was tasked with investigating the reports after Cabinet Secretary Simon Case was removed from the probe after it was revealed he had known about a party held in his own department.
Johnson has faced multiple claims that social events were held inside 10 Downing Street in the run up to Christmas 2020, when local restrictions barred such gatherings.
A Downing Street spokesperson responded to the image saying: “Work meetings often take place in the Downing Street garden in the summer months. On this occasion there were staff meetings following a No. 10 press conference.”
On Monday, Johnson would not elaborate on whether he had already been interviewed by Gray yet.
Angela Rayner, Deputy Leader of the Labour Party and Shadow Chancellor of the Duchy of Lancaster, responding to reports of the email, said: “Boris Johnson has consistently shown that he has no regard for the rules he puts in place for the rest of us.”
“He is trying to get officials to take the fall for his own mistakes, but he sets the tone for the way Downing Street and the rest of government operates,” she added.