The Covid inquiry makes a brief return on Thursday to considering how Westminster and Whitehall responded to the pandemic, as the cabinet secretary, Simon Case, gives evidence delayed for months because of illness. Case had been due to appear before the inquiry in the autumn, when a series of other top officials appeared, as did politicians who were in leading roles during the time of the pandemic, notably the then prime minister, Boris Johnson. But Case, the most senior civil servant in the UK, had to go on medical leave and his testimony was put back. Case figured quite heavily in earlier evidence, and there will be no shortage of things to ask: Does he believe Johnson’s No 10 was “poisonous” and “mad”? The bulk of what we have heard so far from Case has been in WhatsApp messages, some of which have shown a colourful turn of phrase and a very genuine-seeming scepticism about the Johnson administration even before he became cabinet secretary. Probably the most scathing words came in an exchange in July 2020 with Mark Sedwill, whose job as cabinet secretary Case took over two months later. “I’ve never seen a bunch of people less well-equipped to run a country,” Case wrote to Sedwill. Having joined the No 10 staff in May 2020, Case added: “At this rate I will struggle to last six months. These people are so mad. Not poisonous towards me (yet), but they are just madly self-defeating.” Were people wary of joining Johnson’s No 10? Another notable snippet from the Case-Sedwill exchanges was Case’s complaint that it was difficult to recruit new people for No 10 because of the perception of chaos and infighting. Case told Sedwill that Johnson had asked him who would replace Tom Shinner, another senior official working inside No 10 on Covid, adding: “I was quite direct in telling him that lots of the top-drawer people I had asked had refused to come because of the toxic reputation of his operation.” Did Carrie Johnson, the PM’s wife, have undue influence? When asked what the policy was, Case replied: “Whatever Carrie cares about, I guess.” He added: “I was always told that Dom [Dominic Cummings] was the secret PM. How wrong they are. I look forward to telling select cttee [committee] tomorrow – ‘Oh, fuck no, don’t worry about Dom, the real person in charge is Carrie.’” Were people in No 10 “basically feral”? Another set of exchanges between Case and Sedwill showed the pair again bemoaning the Downing Street culture. “It is like taming wild animals,” wrote Case, who was at the time the lead civil servant in No 10. “Nothing in my past experience has prepared me for this madness. The PM and the people he chooses to surround himself with are basically feral.” Sedwill said in reply: “I have the bite marks.”