The UK’s top civil servant Simon Case has announced he will step down at the end of the year on health grounds.

Cabinet Secretary Mr Case, who has been undergoing treatment for a neurological condition, told colleagues “whilst the spirit remains willing, the body is not”.

There have been reports of tensions at the heart of No 10 between Mr Case and Sir Keir Starmer’s chief of staff Sue Gray, but the Cabinet Secretary said: “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.”

Cabinet Secretary Simon Case (Victoria Jones/PA)

Mr Case returned to work in January after two months off sick and he said he had been “undergoing medical treatment for a neurological condition over the last 18 months”.

A recruitment process for the next cabinet secretary has begun.