LONDON - Sir Mark Sedwill, the UK’s most senior civil servant, looks set to announce his departure as early as this week under Boris Johnson’s plans for a Whitehall revolution.

The ousting of Sir Mark will be the most obvious signal that a long-planned shake-up of the Civil Service by Dominic Cummings, Mr Johnson’s chief aide, is gathering pace.

Several sources told The Sunday Telegraph that an announcement would be made about Sir Mark’s future as early as Monday.

Sir Mark was appointed National Security Adviser by Theresa May in 2017 and then was made Cabinet Secretary a year later and controversially allowed to do both jobs.

One source said Sir Mark was “fighting to stay as National Security Adviser” and already seemed resigned to losing his post as Cabinet Secretary.

The source said: “He knows he has lost one half of his job. He is fighting to keep the national security one but they want to take everything off him and give him a non-job.”

Sir Mark was strongly tipped to be heading to Washington to replace Sir Kim Darroch as the UK ambassador when Mr Johnson entered No  10.(FA)