At the time, outdoors gatherings were banned in England under the strict Covid curbs.
Prime Minister’s Principal Private Secretary Martin Reynolds sent the invitation email which has since been leaked to the news organisation.
Among those invited include the Prime Minister’s advisors, speechwriters and door staff.
As obtained by ITV News, the email read: “Hi all, 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!”
It follows allegations of a separate staff gathering in the garden on May 15.
A photograph emerged of Mr Johnson and his wife sat with No 10 staff drinking wine and eating cheese.