BORIS Johnson has appointed "passionate Unionist" Simon Case as Cabinet Secretary and head of the UK Civil Service, the Cabinet Office has confirmed.

The 41-year-old will succeed Sir Mark Sedwill, who announced in June that he would be standing down amid rumours of a rift in 10 Downing Street.

Case, a former private secretary to Prince William, 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.

Currently the permanent secretary in Number 10, his new role will put him in charge of overseeing the day-to-day running of the UK Government and joining it up with the Prime Minister's policy priorities.

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

Apart from his role with Prince William, Case's career has included helping deliver the 2012 London Olympics, a tenure as private secretary to former prime minister David Cameron, and working on the Irish border issue created by Brexit.

Sources told The Spectator that Case is “patriotic to his core” and a “passionate Unionist”.

He was also described as a “bit of a gossip” who has a “slightly pompous” approach.

The news comes as Johnson prepares to visit Scotland for the third time in recent months as Downing Street reportedly changes its strategy on fighting independence.