Boris Johnson has been pictured with wine and cheese alongside his wife and up to 17 staff in the Downing Street garden during lockdown, raising questions over No 10’s insistence a “work meeting” was taking place.

The photograph was shared with the Guardian following No 10’s denial last week that there was a social event on Friday 15 May 2020 including wine, spirits and pizza inside and outside the building. Johnson’s spokesman said Downing Street staff were working in the garden in the afternoon and evening.

However, the picture raises questions over that assertion. Bottles of wine are in evidence, there is a lack of social distancing and 19 people are gathered in groups across the Downing Street terrace and lawn.

At the time social mixing between households was limited to two people, who could only meet outdoors and at a distance of at least 2 metres. In workplaces, guidance said in-person meetings should only take place if “absolutely necessary”.

Angela Rayner, the deputy leader of the Labour party, described the picture as “a slap in the face of the British public”, adding: “The prime minister consistently shows us he has no regard for the rules he puts in place for the rest of us. Alleged drinking and partying late into the evening [at No 10] when the rest of us were only recently getting one daily walk.”

The prime minister has faced a string of allegations of partying and socialising in No 10 while Covid restrictions were in place. He was forced to order a civil service inquiry, though its head stepped down on Friday over allegations of his own Christmas party.

The past week has been described as the worst of the prime minister’s premiership, with a major rebellion by Conservative MPs over Covid regulations followed by a historic byelection defeat and the shock departure of the Brexit minister, David Frost.

In the new image shared with the Guardian, Boris Johnson and Carrie, who appears to be holding their newborn baby, are seen sitting around a table with a cheeseboard and wine, along with two people believed to be a civil servant and an aide. Last week No 10 said Johnson was working in the garden before retiring to his flat at 7pm.

On that day Matt Hancock, then health secretary, had given a 5pm press conference urging people to stick to the rules and not take advantage of the good weather over the May weekend to socialise in groups.

At the time schools were still shut and pubs and restaurants were closed, with strict controls on social mixing. More people had been allowed to return to their workplaces, but guidance said social distancing of 2 metres should be followed at all times and “only absolutely necessary participants should attend meetings and should maintain 2-metre separation throughout”.

The Guardian reported last week, as part of a joint investigation with the Independent, that Johnson had been present for an alleged social gathering in Downing Street on 15 May 2020. Sources said the prime minister had spent about 15 minutes with staff, telling an aide inside No 10 that they deserved a drink for “beating back” coronavirus.

Insiders claimed about 20 staff drank wine and spirits and ate pizza following a press conference on that day, some in offices inside No 10 and others going into the garden. Some staff stayed drinking until late into the evening, they alleged. The sources described the event as having a “celebratory” feel given the initial loosening of some restrictions and the good weather in London that day.

In response, No 10 said Johnson and staff had been working in the garden and made no reference to the allegations of drinking alcohol and socialising. The prime minister’s official spokesperson said last week: “In the summer months Downing Street staff regularly use the garden for some meetings. On 15 May 2020 the prime minister held a series of meetings throughout the afternoon, including briefly with the then health and care secretary and his team in the garden following a press conference.

“The prime minister went to his residence shortly after 7pm. A small number of staff required to be in work remained in the Downing Street garden for part of the afternoon and evening.”

Hancock, who was health secretary before he had to resign after breaking social distancing rules with his aide, Gina Coladangelo, said it was “not true” that he was involved in a social gathering. “After the press conference, which finished at approximately 5.53pm, Matt debriefed his own team, then went to the Downing Street garden to debrief the prime minister. He left Downing Street at 6.32pm and went back to the Department for Health and Social Care,” Hancock’s spokesperson said. There is no suggestion he was drinking or stayed late.

In light of the new picture, it is understood No 10 maintains that people drinking at work was not against regulations at the time. A Downing Street spokesperson said on Sunday: “As we said last week, work meetings often take place in the Downing Street garden in the summer months. On this occasion there were staff meetings after 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.”

There have been a string of accusations that Downing Street staff broke rules by having Christmas parties, with the prime minister presiding over a Zoom quiz and giving a speech at a leaving do.

Johnson ordered an investigation after a video was leaked to ITV showing aides laughing about a Christmas party with wine and cheese, and suggesting passing it off as a business meeting. Simon Case, the cabinet secretary, stepped down from leading that investigation after it emerged his own office had held a Christmas party, and has been replaced by another senior civil servant, Sue Gray.

Rayner said: “This picture is utterly heartbreaking to see for the people that spent the first wave of the pandemic on the frontline of our health service, desperately missing their loved ones, enduring loneliness, missing funerals … Every day that passes seems to add another event to Sue Gray’s growing list of investigations into alleged unlawful gatherings in Downing Street.”

“Boris Johnson’s government is run with the attitude that it is one rule for them, and another for everyone else. He is totally unfit to lead our country.”