The Prime Minister’s most senior aide Dominic Cummings is set to leave Downing Street by Christmas, the BBC has reported.
Mr Cummings had already pledged to make himself “largely redundant” by the end of 2020.
It follows a turbulent week at No 10 in which Lee Cain - the director of communications and an ally of Mr Cummings - also stood down amid reports of internal tensions at Number 10.
The senior aide, who was instrumental in the victory of the leave campaign during the EU referendum, had faced calls to resign earlier in the year after allegedly breaking coronavirus rules during the nation’s first lockdown.
After Boris Johnson became prime minister in July 2019, he hired Mr Cummings to be his senior adviser. and six months later the pair's strategy of stressing "Get Brexit Done" as the main campaign message helped the party win a larger majority in the general election.
Who is Dominic Cummings?
Mr Cummings was brought in to the heart of government as Mr Johnson's chief adviser, when he became PM, given his past record of rubbing senior Tory politicians up the wrong way.
His abrasive style and uncompromising attitude towards those he regards as lazy or intellectually inferior, which would include most MPs, have made him few friends at Westminster.
Mr Cummings has been in and around the upper reaches of government and the Conservative Party for nearly two decades and has made a career out of defying conventional wisdom and trying to upset the established order.
He has never been a member of the Conservative Party and has little time for what he sees as some of the time-servers and publicity addicts that populate the Commons benches.
A longstanding Eurosceptic, he was a director of the anti-euro Business for Sterling group. Cummings's other passion is changing the way government operates.
A native of Durham, in the north-east of England. His father, Robert, was an oil rig engineer and his mother, Morag, a teacher and behavioural specialist.
He went to a state primary school and was then privately educated at Durham School. He graduated from Oxford University with a first-class degree in modern history and spent some time in Russia, where he was involved with an ill-fated attempt to launch an airline, among other projects.