The prime minister and his wife Carrie attended a “bring your own booze” event in the Downing Street garden during the UK’s first national COVID lockdown.
More than 100 employees in Number 10 were invited to the drinks on 20 May 2020.
In what has been described as evidence of “more rule breaking at the heart of government”, an email sent by Martin Reynolds – a key aide to Boris Johnson – invited staff to “make the most of the lovely weather” with “some socially distanced drinks”.
The email, obtained by ITV News, adds to a recent allegation from Dominic Cummings – the prime minister’s estranged former chief adviser – that a drinks event was held in the Downing Street garden.
According to ITV News, Mr Reynolds’ email was sent to more than 100 employees in Number 10, including the prime minister’s advisers, speechwriters and door staff.
It is reported that around 40 staff gathered in the garden that evening to eat picnic food and drink, including Mr Johnson and his wife Carrie.
At the time of the alleged 20 May event, Britons had only recently been allowed to meet with one person from another household outside as long as they remained two metres apart.
Mixing with multiple households was still banned.
Doubts had already been cast over Mr Reynolds’ position in Number 10 following the initial claims of an event on 20 May.
A senior government source told Sky News: “Reynolds job was to protect staff who were looking to him to lead them through something nobody had ever done before, this is just a perfect example of how he failed at it.
“The public are right to be outraged at the one rule for them one rule for us, some people in Number 10 felt uncomfortable about it at the time, but the truth is nobody ever got to grips with working in Number 10 while the rest of the country were made to work from home.
“Reynolds didn’t protect people from the spread of COVID in the building and he and others didn’t think through the consequences of those actions.
“He was in charge of it all, he has to be held accountable for it.”
Labour’s deputy leader Angela Rayner 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.
“At the time this party took place, key workers on the frontline were working round the clock to keep us all safe, people suffered loneliness and loss in unimaginably tough circumstances and for the majority of the country our freedom was limited to a daily walk.”
Number 10 would not comment on the leaked email while an inquiry into multiple allegations of COVID rule-breaking in Downing Street and other government buildings is ongoing.
That inquiry is being led by senior civil servant Sue Gray.