At first glance, it has all the hallmarks of a laid-back post-work social gathering on an uncommonly warm British spring evening. There are 19 people present, sitting or standing in four distinct groups, each one of which appears to have drinks. There are bottles of red wine and a cheeseboard. The event, on Friday 15 May 2020, took place in the garden behind Nos 10 and 11 Downing Street, a mix of terrace, lawn and formal planting that is used variously for formal entertainment, domestic leisure and work. Across England, people were still banned from meeting more than one adult from another household socially – and then it had to be outdoors and at a 2-metre distance. On the terrace in the foreground, sitting at a rectangular garden table surrounded by rattan-style chairs, Boris Johnson chats to his then fiancee, Carrie Symonds, who is cradling what appears to be the couple’s newborn son, Wilfred. On the same table, at which a civil servant and an aide are chatting to each other, is a half-empty bottle of wine, a wine glass and a wooden board with bread and cheese. There are two other small groups – another terrace table of four people, also with wine, and a man and a woman sitting on the grass behind them. There is also a congregation of eight men and one woman standing around an apparently bottle-laden table, also on the lawn. Even if you did not know this was the Downing Street garden, it might be evident these are work colleagues, with most wearing formal office clothes. But the sense of the occasion, as portrayed in the photo, seems very much social. These are, it would seem, people who had been working – in this instance, the then health secretary, Matt Hancock, had fronted a televised Covid press conference in Downing Street at 5pm – but were now winding down afterwards. The presence of Carrie next to her partner, the prime minister, reinforces that sense. Attenders’ body language is relaxed and there are no laptops, files or notepads to take minutes on show. Reports about the evening in question, passed to the Guardian before the photo emerged this weekend, said about 20 staff drank wine and spirits and ate pizza, both in offices inside No 10 and in the garden on 15 May 2020, with some people allegedly staying drinking until late into the night. Presented with the photograph, Downing Street said it showed colleagues having work meetings, which, given the hours involved, sometimes included drinks, and were not against the then regulations. The event took place amid the first lockdown, at which point specific rules against workplace socialising had yet to be set out – but only because people were only supposed to be in work if absolutely necessary. Downing Street staff were permitted to do this, as key workers, but the guidelines on in-person meetings were very clear: these should only take place if absolutely necessary, and then with everyone distanced at least 2 metres. That is very much not happening in the photograph. Ultimately, it will come down to the watching public looking at the photograph, reading the No 10 explanation, and being asked to accept that this was purely a work event. For many, this could feel like quite a leap of faith.