The claim was on Thursday put to Downing Street, where Ms Williams-Walker still works. No denial has been issued.

She was jokingly nicknamed “DJ SWW”, a reference to her initials, according to one present that night.

As the evening wore on, the alcohol still flowing, those celebrating the photographer’s departure headed to the Downing Street garden.

‘Too much wine spilling on No 10’s basement carpet’

One present said there was a fear that too much wine was spilling on the basement carpet as they danced. They are said to have relocated at around midnight.

In the garden, the two groups marking the departure of Mr Slack and the photographer are said to have merged.

The drinking and chatting allegedly carried on into the early hours of the morning. One Downing Street figure had a go on a child’s swing belonging to Wilf Johnson, the Prime Minister’s son, according to one eyewitness, and broke it.

The gathering is the first allegation of lockdown-breaking in Downing Street in 2021 to have emerged, marking a new front in the row engulfing the Prime Minister. Previous party allegations date from 2020.