Civil service chief Simon Case – who described the government as a “terrible, tragic joke” in private WhatsApp messages at the height of the pandemic – is expected to be questioned over a “treasure trove” of further correspondence when he appears before the official Covid inquiry. Case, who became cabinet secretary in September 2020, having previously served as permanent secretary in No 10, will give evidence to Lady Hallett’s inquiry either on 30 or 31 October, or in the first week of November. Sources say that many more messages involving Case will be produced, raising further questions about the quality of government during the national emergency. Hallett’s inquiry is examining questions about “core UK decision-making and political governance” to establish how well the Whitehall machine reacted under huge pressure. Several top Cabinet Office officials and civil servants in key positions at the time will give evidence in the current module of the inquiry, including Case and Boris Johnson’s former principal private secretary, Martin Reynolds – nicknamed “party Marty” – because he organised a “bring your own booze” party in the Downing Street garden during the lockdown. Some astonishingly frank messages from Case were released by the Covid inquiry on Friday. His most damning comments were made in a WhatsApp exchange that included Lee Cain, Johnson’s communications chief, and Dominic Cummings, his senior adviser. In one Case said: “The government doesn’t have the credibility needed to be imposing stuff within only days of deciding not too [sic]. We look like a terrible, tragic joke. If we were going hard, that decision was needed weeks ago. I cannot cope with this.” In other disparaging comments he said Boris Johnson’s wife, Carrie, appeared to be “the real person in charge” of the government. He also wrote that at one point he was “going to scream” after hearing about a plan by former health secretary Matt Hancock to draw up a so-called “regional circuit breaker” to curb the spread of the virus. Case wrote: “I was always told that Dom [Dominic Cummings] was the secret PM. How wrong they are. I look forward to telling select cttee tomorrow … don’t worry about Dom, the real person in charge is Carrie’.” As the inquiry gathers pace both Case and Rishi Sunak are likely to face growing criticism. Daisy Cooper, the Lib Dem health spokesperson, said : “Sunak stood on the steps of Downing Street and promised integrity, yet still sitting around the cabinet table are the very same people responsible for Partygate, the mismanagement of the pandemic. “It’s now clear for all to see that instead of leadership, all that was provided by those in charge was gossipy WhatsApp messages and secret admissions that they were in over their heads. Sunak pretends to offer change but all he offers is an out of touch and incompetent government.” Case has been involved in several controversies since taking the top Whitehall job. As well as being accused of failing to prevent Partygate, he was caught up in the row over a loan facility Johnson was offered with the help of former BBC chairman Richard Sharp. His name cropped up in the row over the redecoration of Johnson’s Downing Street flat, with Case apparently helping to smooth the way for the upgrades to take place. More generally, civil servants have accused him of failing to stand up for officials in the face of repeated criticism and targeting by ministers.