Simon Case is unlikely to be kept on as cabinet secretary under Keir Starmer if Labour wins the next general election, senior party figures have said. Case is understood to be considering his own future after a difficult year in the aftermath of the Partygate scandal and damaging leaked WhatsApps involving the former health secretary Matt Hancock. But Labour sources and shadow cabinet ministers have said Starmer would be likely to appoint a new cabinet secretary upon entering No 10. One questioned why he had not wanted to wait to give the coveted role to the Partygate investigator Sue Gray, who has instead departed a long career in the civil service to be Starmer’s chief of staff in opposition. However, sources with knowledge of Gray’s move said she had wanted a new challenge sooner than the next election. She had recently missed out on the job of permanent secretary of the trade department, but before that had been even more disappointed to miss out on the job of head of the Northern Ireland civil service. Whitehall sources said that had been “the job she really wanted” and that she was more interested in organisation and the workings of government than politics or policy. They also said she had been left “bruised” by the publicity around her decision to work for Starmer, especially coverage related to her son’s connection to the Labour party. Case is regarded within the civil service as having blocked Gray’s chances of promotion. His own future is now in doubt with reports first emerging in the Financial Times that he was considering an early exit as cabinet secretary after being appointed to the role in September 2020 following a stint as permanent secretary of No 10. His time in the job has been marred by the ethics scandals of the Boris Johnson era, including controversies over loans to the then prime minister, and questions over the appointment of Nadhim Zahawi given an investigation into his tax affairs. Case was thought likely to depart as cabinet secretary on the appointment of Liz Truss as prime minister, but his background as a royal aide proved invaluable after the death of the Queen. Rishi Sunak kept him on as cabinet secretary. However, his discretion is now in question after leaked WhatsApp messages revealed by the Telegraph showed that Case described Johnson in one message as a “nationally distrusted figure”, while referring to the then chancellor Sunak’s opposition to Covid restrictions on businesses as “going bonkers”. He also sent a message to the then health secretary, Hancock, saying it was “hilarious” that some travellers were being “locked up” in hotels after entering the UK. Sunak launched a full-throated defence of his embattled cabinet secretary on Tuesday – although he refused to guarantee Case would still be in his job come the next election. The prime minister said: “The cabinet secretary has done a great job. He has worked very hard to support the government’s agenda, particularly on the issue of tackling illegal migration. “The cabinet secretary has been at the heart of coordinating our work. I’m very grateful to him. And I look forward to working with him for a very long time to come, quite frankly.” Since the emergence of his messages with Hancock, former senior civil servants have expressed surprise and concern at his “unprofessional” and jokey WhatsApp chats during the Covid crisis, saying they appeared to be a highly unusual departure from normal standards. No 10 said on Monday that Sunak had full confidence in Case. The Cabinet Office had no comment. However, a friend of Case said over the weekend: “I’m sure he will be embarrassed by these remarks, but they were made in the heat of the moment in the middle of a national crisis responding to a cabinet minister. They do not represent the full policymaking process. We are talking about casual language being used in a casual setting here.”