Cabinet Secretary Sir Jeremy Heywood diagnosed with cancer during summer political turmoil

Sir Jeremy discovered he had the illness in June and was treated in the following months

Sir Jeremy Heywood received treatment in early autumn (Getty Images)

The most senior civil servant was diagnosed with cancer and underwent treatment while continuing to work through the summer's political turmoil.

Cabinet Secretary Sir Jeremy Heywood discovered he had the illness in June and received treatment up until early autumn.

It would have coincided with a period following the election when it was not clear if Ms May's administration would survive with civil servants having to be ready for any potential change.

A statement said that with the full support of his doctors, "Sir Jeremy has continued with his normal duties for the Prime Minister and Cabinet, and as Head of the Civil Service."

It went on: "He remains totally focused on those duties and we will be making no further comment on this private matter."

The election took place on June 8 with the Sir Jeremy needing to ensure that the work of government continued unhindered, despite the precarious position of Ms May after she lost the Conservative's Commons majority.

Sir Jeremy was appointed Cabinet Secretary following the announcement of Sir Gus O’Donnell’s retirement in December 2011. From September 2014 Jeremy also took on the title Head of the Civil Service.

He has worked closely with four prime ministers, under Tony Blair he was Principal Private Secretary before becoming Permanent Secretary at Number 10 to both Gordon Brown and David Cameron.

As the civil service chief, Sir Jeremy has been heavily involved in preparations for leaving the European Union, a process which is set to significantly add to the workload of British officials as responsibilities come back from Brussels.