When Dominic Cummings left Downing Street in November 2020, it was meant to be an amicable departure from Boris Johnson. But it soured within days, amid a briefing war. The prime minister’s former chief aide and his allies were described as presiding over a “macho culture” at No 10. Cummings is said to have reacted to the negative stories by warning Johnson: “I have never briefed against you: believe me, when I do, you’ll fucking know about it.” In that sense, Cummings has certainly been true to his word. Key advisers, bound usually by a residual loyalty, normally remain relatively quiet after they depart a prime minister’s side. But Cummings has always been different, and armed with his knowledge of a year and a half at the very top of government, he has been willing to fight back ever since. It was Cummings who prompted Johnson’s most serious crisis yet. Last week he revealed in a blog that, on 20 May 2020, “a senior No 10 official invited people to ‘socially distanced drinks’ in the garden”. That posting was, in part a response, to the Guardian publishing a picture of Johnson, Cummings and others chatting over cheese and wine in Downing Street on 15 May 2020. The photo in the Guardian had appeared a week before Christmas, following weeks of revelations across the media about lockdown-breaching parties at Downing Street. Cummings insisted this gathering was a work meeting and that somebody, possibly the prime minister himself, “brought a bottle of wine out to the table”. This rebuttal was published on 7 January, just as the political year had begun to restart. Three days later came another revelation. On Monday, ITV published the now infamous invitation from Johnson’s principal private secretary, Martin Reynolds, who emailed more than 100 staff inviting them to drinks in the Downing Street garden on 20 May 2020. Within about half an hour of ITV’s report Cummings tweeted to say Johnson himself was present, using the shopping trolley emoji he uses to describe his former boss.In evidence to MPs last May, he accused Johnson of being so indecisive he ends up “smashing from one side of the aisle to the other”. With other sources confirming Johnson’s presence at the gathering 18 months ago, the prime minister had little choice but to apologise in the Commons on Wednesday, although he insisted the event “could be said, technically, to fall within the guidance” of the time as it had taken place at work, even if it was the Downing Street garden. Not so said Cummings, tweeting his reply a few minutes after Johnson delivered his statement. In a potent mixture of upper and lower case, Cummings wrote: “The invite = obv totally SOCIAL NOT WORK. (UNlike all the mtngs in garden). No way ‘technically within rules’.” It was he added “bullshit cos altern[ative] is admit he broke rules + resign”. The timing of the 20 May party may also explain why Cummings was not immediately fired by Johnson when two days later it emerged that his then chief aide had travelled to Durham in March that year, despite having symptoms of coronavirus. Instead the prime minister forced him to explain himself in person – in the Downing Street garden. Few believe that the public briefing will stop here. “Cummings is the kind of person who, once he focuses on something keeps going and going until he feels he has won,” said one former political associate who worked with him on the Vote Leave campaign in 2016. “It’s what makes him difficult and what makes him brilliant.”