The UK’s most senior civil servant is considering an early departure from his role after leaked WhatsApp messages that have infuriated Conservative MPs.

Simon Case, cabinet secretary, has told friends that he is “genuinely undecided” between trying to guide the civil service through a general election next year and resigning this year to give his successor a chance to bed in before the possible formation of a new government.

Case has come under pressure from Conservative MPs this week over WhatsApp messages that appeared in The Telegraph as a part of a trove of leaked material.

In the messages, Case describes some opposition to Covid-19 restrictions as “pure Conservative ideology”. When designing a communications strategy, Case said that then prime minister Boris Johnson, who had poor personal polling, was “nationally distrusted”.

“I can’t see how Simon Case survives this, especially if there are more messages of his directly slagging off other ministers,” one senior Conservative backbencher told the Financial Times.

While friends of the cabinet secretary say that he has continued to receive support from his colleagues, he is also said to be “fed up”.

Among Case’s fellow officials, there is particular concern about his handling of “partygate”, which centred on rule-breaking in Downing Street and Whitehall during Covid restrictions in 2020 and 2021.

One senior official said: “Simon didn’t stand up for his own people over partygate,” adding that junior staff were issued with fines for attending events happening on his watch.

Case has also drawn scrutiny for his knowledge of Johnson’s personal financial relationship with the chair of the BBC and for the government’s response to bullying allegations against Dominic Raab, the justice secretary.

Rishi Sunak’s spokesperson declined to comment on the WhatsApp messages. Downing Street said: “The cabinet secretary has the confidence of the prime minister and that has not changed.”

An ally of Case said they contained “casual language being used in a casual setting . . . There are a lot of Conservatives who dislike the civil service, but who can name only one civil servant.” Another ally of Case said that his “original sin was being young and talented and promoted to that job before he was grey”.

Another issue upsetting officials was the removal of Tom Scholar, the former permanent secretary of the Treasury, by Kwasi Kwarteng, who briefly served as chancellor in Liz Truss’s shortlived government. This was regarded as inappropriate over-reach by ministers. Case, however, is known to be wounded by the implication that he failed to support Scholar.

A Cabinet Office insider said they considered a departure this year as very unlikely.

Another senior official said: “The charge sheet is now so long against him, the only interpretation can be that the PM probably doesn’t want to get rid of him.”