Boris Johnson appoints new Cabinet Secretary who worked on Irish border issues created by Brexit

The 41-year-old will succeed Sir Mark Sedwill, who announced in June that he would be standing down.

Mr Case, a former private secretary to the Duke of Cambridge, takes on the job as the country’s top civil servant as the shake-up of Whitehall under Boris Johnson and adviser Dominic Cummings continues.

He will be responsible for overseeing the day-to-day running of the Government and joining it up with the Prime Minister’s policy priorities.

His appointment follows five departures of senior civil servants this year alone, under the so-called “hard rain” overhaul reportedly orchestrated by Mr Cummings, Mr Johnson’s de facto chief of staff.

The Prime Minister said: “Simon will make a fantastic Cabinet Secretary and head of the Civil Service.

“His years of experience at the heart of government and working for the royal household make him ideally suited for this crucial role.

“I would also like to thank Mark Sedwill for his outstanding service to the Government and the country as a whole.”

Before taking up his duties at Kensington Palace in 2018, Mr Case was one of the UK’s lead officials working on the border issues between the Republic and Northern Ireland created by Brexit, during his term as the director-general Northern Ireland and Ireland in the Department for Exiting the EU.

In March 2017 he was appointed director-general at the UK Permanent Representation to the EU for the UK-EU Partnership, a role which saw him lead “the UK Government’s work on exiting and seeking a new partnership with the European Union”.

He also served as principal private secretary to David Cameron when he was prime minister and to his successor Theresa May between 2017 and early 2017.

A doctor of philosophy, the Cambridge-educated Mr Case joined the Civil Service in 2006 and was previously director of strategy at the intelligence and security organisation GCHQ from 2015 to 2016.

His promotion to Cabinet Secretary comes after Sir Mark Sedwill announced he would step down from the post amid reports of clashes with Mr Cummings.

Mr Case is the youngest Cabinet Secretary since 1916 and is reportedly younger than all permanent secretaries bar one, according to The Times newspaper.