As Christmas parties go, it may not be everyone’s idea of a good time: there are barely touched canapes, hotel buffet-style containers of hot food, a hand sanitiser dispenser visible in the background, and about 25 political activists, all crammed into a brightly lit basement in the middle of a pandemic. Uninspiring though it might be, that is the scene captured by a photo taken at Conservative campaign headquarters (CCHQ) last December, which emerged in the Daily Mirror on Tuesday to create another political nightmare for Boris Johnson. On Wednesday, guests at the party – hosted by the campaign for Shaun Bailey, then the Conservative mayoral candidate for London – were grappling with a hangover that took a year and a day to hit. Bailey himself, who had already stood down as chair of the London assembly’s police and crime committee, issued an “unreserved apology” before noting that the “gathering” was “held by some of my staff”, adding that he left shortly after delivering a speech of thanks. Meanwhile, several attenders identified by the Guardian – variously wearing spangly braces, party hats and Christmas jumpers – appeared to have quickly deleted their social media profiles. One, a councillor, was the subject of a clarifying statement from his local Conservative group, which said that he had already decided not to stand again. Another, who ran Vote Leave’s video ads during the Brexit campaign, deleted his WhatsApp profile picture after being asked for comment. Several of those present were staff seconded from CCHQ and had faced disciplinary action, the cabinet minister Grant Shapps said on Wednesday, calling the event “disgraceful”. The event – described by the Times as “raucous” in a report last week which also said that an office door was damaged – took place on 14 December last year. At that time, London was subject to tier 2 restrictions which prohibited indoor social mixing between different households. Shortly before the event took place the government announced that London would move into tighter tier 3 restrictions. The change came into force two days later. While Conservative sources moved to blame the Bailey campaign alone for the CCHQ event after the picture first emerged, it is understood that Conservative party CEO, Darren Mott, became aware of the event and expressed his displeasure. The campaign is understood to have organised outside catering. A Conservative party source told the Guardian that the four party staffers involved were disciplined just over a week after the event took place. Some members of the Bailey campaign are thought to have declined their invitations. To the immediate right of Bailey in the picture is Nick Candy, the property developer and prominent Tory donor, raising a glass of wine. A spokesperson for Candy, who is married to the Australian actor and singer Holly Valance, told the Mirror that he was there for an “end of year review” and gave a “short thank you speech” to the team before leaving soon after. Immediately next to Bailey on his other side is Adam Wildman, a Conservative councillor in the London borough of Bexley. According to his LinkedIn profile, Wildman was political director of the Conservative party until May this year when he joined the PR and consultancy firm Teneo as an associate director. His Twitter profile, which described him as a “recovering policy wonk”, was no longer available on Wednesday. He did not immediately respond to a request for comment. On Wednesday afternoon a statement on behalf of Bexley’s Conservative councillors expressed “shock and disappointment” at the picture. It added: “Following our selection process earlier this year, Councillor Wildman took the decision not to stand for the Conservatives again at the election in May 2022.” Alexander Thompson, who was entrusted by Dominic Cummings with masterminding Vote Leave’s video ads at the age of 25, is also in the picture. In a 2016 piece for Newsweek, he castigated the advertising industry, which he said largely backed Remain, as out of touch, casting them as “beardy hipsters” enjoying themselves in London while people in the rest of the country worried for their children’s health. Thompson, who is at the rear centre of the picture in a red crown, beard and glasses, hung up when asked for comment on Wednesday before deleting his WhatsApp picture shortly after receiving a follow-up message. Ben Mallet, Bailey’s campaign director, is lying on the ground at the front of the picture, wearing red patterned braces and holding a glass of wine. His Twitter profile also appeared to have recently been deleted. He declined to comment personally, but shared an apology on behalf of the campaign which called the gathering “a serious error of judgment”. In front of Bailey, wearing what appears to be a festive headdress, is Malin Bogue, an aide to his mayoral campaign. She was previously director of special projects, on a voluntary basis, during Boris Johnson’s successful bid to become Conservative leader in 2019. She declined to comment when approached by the Guardian but shared the same comment as Mallet. Bailey’s agent Kerry Halfpenny, whose name appeared on Bailey campaign materials criticised for obscuring his status as a candidate in the mayoral election, is to the right of Candy in a patterned dress. She also declined to comment. Four other junior campaign aides and political staffers did not respond to requests for comment. Three of them also deleted their Twitter or LinkedIn profiles.