Number 10’s communications director Lee Cain is the latest in a group of high profile departures under Boris Johnson, amid reports of increasing tension inside Downing Street.
Which other top figures have left this year and what has been said about their departures?
Lee Cain – communications director
The sudden announcement of Mr Cain’s resignation came less than 24 hours after reports that he would become the Prime Minister’s chief of staff.
The former journalist, reported to be a close ally of chief adviser Dominic Cummings, said he would be leaving Downing Street at the end of the year and had taken the decision after “careful consideration”.
Following the announcement, Boris Johnson said that Mr Cain had been “a good friend and ally” and would be “much missed”.
“I want to thank Lee for his extraordinary service to the Government over the last four years,” he said.
“He has been a true ally and friend and I am very glad that he will remain director of communications until the new year and to help restructure the operation.”
Sir Jonathan Jones – Government legal department
The Attorney General’s office declined to confirm why Sir Jonathan had chosen to leave, but his departure comes after the Financial Times reported he was in a dispute with Downing Street over concerns the Prime Minister wanted to row back on parts of the Brexit deal relating to Northern Ireland.
Following his departure, Labour’s shadow attorney general Lord Falconer tweeted: “Jonathan Jones impressive lawyer and very decent person. Loyal civil servant.
“If he can’t stay in the public service, there must be something very rotten about this Government.
“Reckless, law breaking, trashing the best of the UK.”
Jonathan Slater – Department for Education
The permanent secretary at the Department for Education, Jonathan Slater, stood down when Mr Johnson “concluded that there is a need for fresh official leadership” after the A-Level results controversy.
His departure came a day after Sally Collier resigned from her role as head of exams regulator Ofqual.
Sir Mark Sedwill – Cabinet Office
Sir Mark Sedwill announced his departure from the role of Cabinet Secretary in June amid reports of clashes with Mr Cummings, the Prime Minister’s de facto chief of staff.
He has been replaced as the country’s top civil servant by Simon Case, and said in July that “demoralising” anonymous criticism of officials has “risen in the last few years”.
Sir Mark, in the speech at Oxford University’s Blavatnik School of Government, said anonymous briefings are “damaging” to the process of governance because officials need the support of their leaders.
Sir Mark will also be replaced as national security adviser by Mr Johnson’s chief EU negotiator David Frost.
Sir Simon McDonald – Foreign Office
The Foreign Office’s most senior civil servant, Sir Simon McDonald, seen as a Brexit critic, was told he had to step down before the department was merged with the Department for International Development (DfID).
After he stepped down in June, it was announced in early August that Sir Philip Barton had been appointed as the senior civil servant chosen to head the new Foreign, Commonwealth and Development Office.
Sir Richard Heaton – Ministry of Justice
The permanent secretary’s departure was confirmed in July with his term due to end in August.
Sir Philip Rutnam – Home Office
In February this year, the top civil servant at the Home Office, Sir Philip Rutnam, resigned, accusing Home Secretary Priti Patel of bullying.
Sir Philip, who was the Home Office’s permanent secretary, quit after accusing Ms Patel of a “vicious and orchestrated briefing campaign” against him.