Cabinet Secretary Sir Jeremy Heywood takes leave of absence for cancer treatment

The UK's most senior civil servant discovered he had the illness last year

Sir Jeremy Heywood, the head of the civil service, is taking a leave of absence (Getty Images)

The UK's most senior civil servant will take a three-month leave of absence to receive treatment for cancer and a related infection.

Sir Jeremy Heywood is standing down with immediate effect and will be replaced by the national security adviser, Sir Mark Sedwill, until he returns to work in September.

The cabinet secretary discovered he had the illness in June last year but continued to work during a summer of political upheaval triggered by the shock general election result.

Theresa May had to scramble to form a confidence and supply agreement with the Democratic Unionist Party (DUP) after she lost her parliamentary majority in the snap poll, forcing the civil service to prepare for every eventuality.

A cabinet office spokesperson said: "Jeremy Heywood, the cabinet secretary and head of the civil service, announced today that with the support of the prime minister he will be taking a leave of absence from his current role to have further treatment for the cancer diagnosed last summer and for a related infection."

His role will be shared between Sir Mark, who will take on the formal responsibilities such as attending cabinet meetings, and John Manzoni, chief executive of the civil service, who will lead on managerial issues.

As head of the civil service, Sir Jeremy has played a key role in the Brexit preparations, as Whitehall officials will have to take on a raft of extra responsibilities when Britain leave the European Union.

He was appointed cabinet secretary, Ms May's most senior policy advisor, on the news of Sir Gus O’Donnell’s retirement in 2011. He became head of the civil service in 2014.

Sir Jeremy has worked for four prime ministers, acting as principal private secretary for Tony Blair before becoming permanent secretary at Number 10 to both Gordon Brown and David Cameron.