Boris Johnson has defended a picture of himself and Downing Street staff with cheese and wine in the No 10 garden at a time of tight restrictions on social gatherings.

The prime minister insisted that the photograph taken on May 15, 2020, showed “people at work, talking about work”.

The picture apparently taken from inside Downing Street showed 19 people – including Mr Johnson and his wife Carrie – enjoying wine and cheese with little sign of social distancing and no notebooks or laptops in evidence.

Confronted on Monday about what they were doing, Mr Johnson said: “Those were people at work, talking about work.”

Asked if he normally has meetings with cheese and wine, he said: “These are meetings of people at work. This is where I live, it’s where I work. Those are meetings of people at work, talking about work.”

Mr Johnson’s explanation appeared to contradict comments made by his deputy prime minister Dominic Raab earlier on Monday. The senior cabinet minister suggested that the gathering was held “after” work had finished.

Mr Raab also defended the event, insisting it complied with social mixing rules during the first lockdown because the Downing Street garden is “used for work meetings”. But he admitted: “Sometimes they’ll have a drink after a long day or a long week.”

The No 10 garden gathering during lockdown last May likely broke Covid regulations, top legal expert Adam Wagner said on Monday.

Adam Wagner, the human rights barrister and leading expert on Covid regulations, told Sky News: “Having heard Dominic Raab say that this was a drink after the formal business event had ended – it doesn’t sound convincing as a work gathering. It sounds a lot like a social gathering.”

The barrister said Covid laws meant people were only allowed people to mix for work “where it could not reasonably be done at home”.

Labour leader Keir Starmer said on Monday that it was “a real stretch to pretend that is a work meeting” – noting the photo leaked to The Guardian was taken during a period where people could not attend funerals of loved ones.

“I think there are very serious questions to be answered,” said Mr Starmer. “Just look at the photo and ask yourself is that a work meeting going on or is that a social event? I think the answer is pretty obvious.”