Boris Johnson says a photo of him, his wife and 17 staff members in the Downing Street garden with bottles of wine and a cheeseboard shows "people at work".
The Guardian, which published the image, said the gathering took place in May 2020, after a press conference held during the first lockdown.
At the time, there were strict restrictions on mixing.
No 10 said work meetings often took place outside during summer months.
Asked about the image on Monday, Mr Johnson told reporters: "Those were people at work, talking about work."
Pressed on whether it was acceptable for people to be drinking whilst working, he replied: "I have said what I have to say about that."
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Earlier, deputy Prime Minister Dominic Raab suggested the event took place after work, telling BBC Breakfast: "Sometimes after a busy working day people have a drink - that was not against the regulations."
Labour leader Sir Keir Starmer said it was "a stretch" to call the gathering a work meeting, pointing to the "contrast" between the picture of the PM and people who were unable to attend funerals at the time because of the lockdown.
An investigation is currently taking place into a number of alleged parties in government buildings - including Downing Street - in November and December last year.
The 15 May photograph shows a gathering of staff in the Downing Street garden following a news conference held by then-Health Secretary Matt Hancock, according to the Guardian.
Media caption,
Deputy Prime Minister Dominic Raab defended the lockdown photo
A No 10 spokesman said: "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."
They added: "Downing Street is the prime minister's home as well as his workplace. The prime minister's wife lives in No 10 and therefore also legitimately uses the garden."
SOURCE : BBC
