Mr Case is facing calls to quit from Tory MPs following the emergence of Whatsapp messages where he was highly critical of Boris Johnson and Rishi Sunak, while also mocking holidaymakers forced to quarantine during the pandemic.
There are already deep misgivings about Whitehall’s most senior civil servant within the civil service itself, with many officials believing he had failed to stand up for them in the aftermath of the partygate scandal.
One former permanent secretary told i that the leaked Whatsapp messages showing exchanges between Mr Case and several Cabinet ministers during the height of the pandemic were “completely inappropriate”.
“He should be keeping a proper distance between his role as Cabinet Secretary and theirs as politicians,” the former mandarin said.
“How can he speak truth to power if he presents himself as one of their gang? It shows just how inexperienced and unsuitable for the job he has been.”
Mr Case has come under sustained criticism since the Daily Telegraph published extracts from tens of thousands of leaked messages, after it showed him describing Mr Johnson as a “nationally distrusted figure” and Mr Sunak as going “bonkers” about contact tracing.
He also described the plight of holidaymakers being forced into budget quarantine hotels as “hilarious”.
Former officials from No 10 and the Treasury have claimed that Mr Case is “not hugely well liked” and that his oversight of ministerial appointments in the last 12 months has been questionable, with one former staff member stating he has “not handled events of the last year well”.
He is under increased scrutiny over his handling of Nadhim Zahawi’s appointment as chancellor and Conservative Party chair when he was under investigation by HM Revenue and Customs over his tax affairs.
He is also facing criticism over his handling of complaints about Justice Secretary Dominic Raab, who is under investigation for a string of allegations of bullying. Mr Raab denies allegations of bullying.
In what is being viewed as an attempt to rebuild his trust among civil servants, Mr Case raised his concerns about a Conservative Party email under the name of Home Secretary Suella Braverman which accused officials of standing in the way of efforts to stop the Channel boat crossings.
The latest reports about him suggest Mr Case described himself as “Mr Killjoy” in meetings with “bouncing Boris J” because the then-prime minister was too optimistic about the economy during the pandemic.
He made the remark after telling Mr Hancock in a June 2020 exchange that he had got “stuck with PM enthusing about how there were great opportunities ahead for the UK economy”, adding a facepalm emoji.
Despite the reports, the Prime Minister has backed the beleaguered Cabinet Secretary, telling a press conference this week that he “works very hard to support me, to support the Government’s agenda”, adding: “I look forward to working with him for a very long time to come, quite frankly.”