Dominic Cummings has left Downing Street after internal battles over his role as Boris Johnson's chief adviser.
UK Prime Minister Boris Johnson (right) and his special adviser Dominic Cummings. Photo: Daniel Leal-Olivas / AFP
The BBC understands he will continue to work from home, on issues such as mass coronavirus testing, until the middle of December.
The prime minister is said to want to "clear the air and move on".
Cummings has been at the heart of a No 10 power struggle, which has also seen communications director Lee Cain leave.
Several Tory MPs have welcomed the pair's departure as a chance for Mr Johnson to make a fresh start.
BBC political editor Laura Kuenssberg said Cummings' departure from No 10 had been brought forward given the "upset in the team" in Downing Street, for which she said it had been a "difficult week".
She said there had been long-running tensions between different factions in No 10 but this "slow burning fuse exploded fast when it finally happened".
Cummings and Cain are long-time colleagues, having worked together on the Leave campaign during the EU referendum.
When Cain's exit was announced on Wednesday, it prompted rumours that his ally would also step down.
In response, Cummings told the BBC "rumours of me threatening to resign are invented" but said his "position hasn't changed" since he wrote in January that he wanted to make himself "largely redundant" by the end of 2020.
'Different approach'
Pending what is expected to be a wide-ranging shake-up in No 10, Lord Lister - a close ally of Johnson's who served as his deputy when he was London mayor - has been named interim chief of staff, a position which had been vacant.
Johnson worked with Cummings on the 2016 Vote Leave campaign and hired Cummings to be his senior adviser, when he became prime minister.
Six months later the pair's "Get Brexit Done" campaign message helped Johnson win a large majority in the general election.
Cummings became more of a public figure in the past year and was forced into holding his own news conference at Downing Street in the summer, following controversy over him making a trip to the north of England when non-essential travel was banned at the height of the coronavirus lockdown.
He had a notoriously difficult relationship with Conservative MPs, several of whom have welcomed his exit and said it was time for things to be done differently in Downing Street.
Demonstrators march with an effigy depicting Boris Johnson as a puppet operated by Dominic Cummings, during a rally in London in 2019. Photo: AFP
"Both Dominic Cummings and Lee Cain were pretty dismissive of backbenchers and sometimes ministers and secretaries of state, and I don't think that was helpful," said former Northern Ireland secretary Theresa Villiers.
"I do think it's important that whoever takes over has a different approach."
Sir Bernard Jenkin said it was time to restore "respect, integrity and trust" between No 10 and Tory MPs while veteran Conservative MP Sir Roger Gale said it was "an opportunity to muck out the stables".
Labour said the PM could "rearrange the deckchairs all he wants... but the responsibility for this government's incompetence still lies firmly at Boris Johnson's door".
"The fact there is no plan and no focus in the government's response to Covid is entirely down to him," a party source said.
Who is Dominic Cummings?
* Dominic Cummings, 48, ran the pro-Brexit Vote Leave campaign in the EU referendum and was behind the group's "take back control" slogan
* Prior to the referendum he worked for Iain Duncan Smith when he was Conservative Party leader and Michael Gove at the Department for Education
* Born in Durham, Cummings went to a state primary school before being privately educated at Durham School. He graduated from Oxford University with a first-class degree in modern history
* A longstanding Eurosceptic, he cut his campaigning teeth as a director of the anti-euro Business for Sterling group and once ran a successful campaign to oppose a regionally elected assembly in north-east England
- BBC