Britain's Guardian newspaper on Sunday published a photograph of Prime Minister Boris Johnson and more than a dozen other people drinking wine in the garden of his Downing Street residence which it said was taken during a Covid-19 lockdown in May 2020.
In response, his office said there were staff meetings in the garden that day.
Johnson has been hit by a string of media stories in recent weeks over alleged Christmas parties in government offices, including his own, last year in breach of Covid-19 lockdowns and has ordered an investigation.
The reports have dismayed voters who were told by government to sacrifice their own Christmas events last year, and who face the possibility of being told to curb their Christmas plans for a second year running as the Omicron variant spreads rapidly.
The picture published by the Guardian was reported to be from May 2020, not long after Johnson was discharged from hospital where he had spent several nights in intensive care with Covid-19.
It shows Johnson with his wife Carrie, who appears to be holding their newborn son, and two other people at a table on a terrace in the Downing Street garden with cheese and wine.
Nearby is another table of four other people, and a short distance away are a larger group standing on the grass around a table with bottles of wine.
Asked about the picture, a Downing Street spokesperson 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."
"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."
The newspaper said the photograph was shared with it after Johnson's office last week denied a social event had taken place, saying Downing Street staff were working in the garden in the afternoon and evening.
On that day then health secretary Matt Hancock had given a press conference urging people to stick to the rules and not take advantage of the good weather over the weekend to socialise in groups, it reported.