The cabinet secretary, Simon Case, has announced he will stand down as the UK’s most senior civil servant at the end of the year. In an email to the civil service, Case, who has served four prime ministers and 120 cabinet ministers in the role, said he would stay in post while the process to replace him began. His long-planned departure on health grounds comes after a turbulent few weeks for the Downing Street operation marked by damaging leaks and internal rows, and Keir Starmer is understood to have grown increasingly frustrated. Cabinet ministers and senior aides have urged the prime minister to “get a grip” on the situation to avoid it undermining the government. The departure of Case, who is said to have had a tense relationship with Starmer’s chief of staff, Sue Gray, gives the prime minister the opportunity for a reset. Starmer thanked Case for his support and “years of service to our country” after the announcement, saying: “We are losing a public servant of the highest calibre. “It is right that Simon takes time now to focus on his health, and he should know that he does so with the well wishes of this government and all those who he has served during a truly remarkable career.” Case had already acknowledged he intended to leave in the new year for health reasons, but the lack of a formal announcement meant No 10 had been unable to properly start the hunt for a successor. In his message to the civil service, Case said: “As many of you know, I have been undergoing medical treatment for a neurological condition over the last 18 months and, whilst the spirit remains willing, the body is not. “It is a shame that I feel I have to spell this out, but my decision is solely to do with my health and nothing to do with anything else.” During his four-year tenure, Case has overseen the government’s response to the Covid pandemic and the cost of living crisis, and represented the civil service as it regularly came under attack from senior Conservative party advisers and cabinet ministers. However, he faced criticism after he avoided any sanction for the Partygate scandal while dozens of junior civil servants had to pay fixed-penalty notices. He also came under fire for deleting WhatsApp messages during the Covid crisis, although the Covid inquiry published others, including his description of the then government as a “terrible, tragic joke”. In his email, Case wrote: “We should resist the temptation to become the arbiters of, or participants in, legitimate democratic debate, leaving party politics to politicians and demonstrating our enduring and profound belief in democracy through the service of the elected government of the day.” The Guardian reported last week that the situation in No 10 was likely to come to a head after Starmer returned from his trip to the United Nations in New York, amid dismay at tensions across the government involving Gray. Starmer is being privately urged to appoint a new cabinet secretary from outside the civil service who can “break the mould” of the traditional role, as internal battles continue over Case’s replacement. The job advert for his replacement in the £200,000 role was posted on Monday. The top specification is “the ability to secure the confidence of the prime minister and the cabinet”. Oliver Robbins, the former Brexit negotiator who is close to Gray, has long been tipped to head the civil service. Others within Whitehall who insiders have named as contenders are Tamara Finkelstein, the permanent secretary at the Department for Environment, Food and Rural Affairs, and Jeremy Pocklington, who runs the Department for Energy Security and Net Zero. Case was born and privately educated in Bristol. At university in Cambridge, he studied the history of the intelligence services as part of his undergraduate degree and did a PhD at Queen Mary University of London under the political historian Peter Hennessy, who described him as having a “muscularity of mind and an intellectual curiosity which was outstanding”. Case, who is married and has three daughters, might have been expected to join the security services, but in 2006 he joined the civil service, rising to senior security roles under David Cameron in No 10. He was lured over as director of strategy at GCHQ in 2015 but lasted less than a year before he returned to Cameron as principal private secretary. Case was reportedly close to Cameron, but less friendly with Theresa May. Under her, he was given another difficult job: finding a solution for the Irish border post-Brexit. By 2018, in the depths of Brexit chaos, Case became private secretary to Prince William. Just over two years later he was back in No 10 with the trickiest brief of all: cabinet secretary for Boris Johnson. He was kept on by Liz Truss and Rishi Sunak, but the arrival of a Labour administration – and his own ill health – meant it was time to move on.