The UK’s top civil servant, Simon Case, has returned to work following illness and could be called to give evidence to the Covid inquiry about his scathing views on Boris Johnson’s administration.

Mr Case stepped back from his role as Cabinet Secretary in October due to a medical matter, and did not appear at the Covid inquiry hearings when other senior Westminster figures gave evidence.

But WhatsApp messages disclosed at the hearings showed his exasperation with the sometimes chaotic handling of the pandemic during Mr Johnson’s time as prime minister.

In July 2020, before he became Cabinet Secretary, Mr Case said “I’ve never seen a bunch of people less well-equipped to run a country” in a message to Lord Sedwill, who was the civil service chief at the time.

He also described Mr Johnson and his inner circle as “basically feral”.

And he suggested that Mr Johnson’s wife Carrie was “the real person in charge” in No 10.

In June 2020, Mr Case accused Rishi Sunak of “totally outrageous” behaviour while he was chancellor, complaining that the now-Prime Minister apparently criticised the lack of enforcement of Covid rules but had been instrumental in blocking powers to do so.

UK Covid-19 Inquiry chairwoman Baroness Hallett excused Mr Case from giving evidence due to ill health during the hearings on the Government’s decision-making late in 2023.

But in a ruling in November she said “it very much remains my intention that Mr Case should give oral evidence to the inquiry”.

She order that Mr Case’s lawyers provide the inquiry with an updated report on his ability to give oral evidence at the end of January 2024 or upon his return to work, whichever was sooner.

Downing Street confirmed that Mr Case had now returned to work, paving the way for him to appear at the inquiry.

“He has returned to his full role,” the Prime Minister’s official spokesman said.

It will now be a matter for the UK Covid-19 Inquiry to contact him to give evidence but the spokesman said Mr Case stands ready to appear if called.