Lee Cain, Number 10’s director of communications, has resigned amid a bitter internal power struggle at the heart of Downing Street.
In his resignation statement, Mr Cain - who will stay in his post until the end of the year - confirmed he had been offered a promotion to the key position of the Prime Minister’s chief of staff.
His departure sparked speculation he could be followed by Dominic Cummings, the Prime Minister’s top adviser seen as the most powerful figure in No 10. The two men had worked together on the 2016 EU referendum campaign fronted by Mr Johnson and are regarded as close political allies.
But while Mr Cummings was said to be unhappy at the way his friend had been treated, it was reported he had decided to stay on for now to work on the Government’s response to the coronavirus – in particular the acceleration of the mass testing programme.
Here is everything you need to know:
Who is Lee Cain?
Lee Cain, a long-term ally of Boris Johnson, began his career in local news before becoming a tabloid journalist, working for titles including the Sun and Daily Mirror.
While working at the Mirror, he memorably dressed up as a chicken and followed David Cameron in the run-up to the 2010 election.
He went on to become head of communications at the the Vote Leave campaign, where he worked closely with Mr Cummings. After the Brexit referendum, he worked as a special adviser for Mr Johnson at the Foreign Office.
The spin doctor stuck with Mr Johnson when he quit two years later over Theresa May’s proposed Brexit deal and worked on his successful campaign to succeed her as Tory leader.
When Mr Johnson became Prime Minister, Mr Cain became his head of communications.
Following the announcement of Mr Cain's resignation, Mr Johnson said that he 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.”
Why is Mr Cain controversial?
Along with Mr Cummings, Mr Cain was one of the key players in the Vote Leave campaign for Brexit who were brought into Government by the Prime Minister.
He fought a divisive battle with the press which culminated in a walkout by senior members of the lobby – the reporters covering Westminster – after journalists from some outlets were banned from a briefing on UK-EU trade talks.
The coronavirus crisis has also seen a series of communications missteps, with information affecting the lives of millions of people leaked out or selectively briefed before being formally announced.
Why did he resign?
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.
In his resignation statement, Mr Cain confirmed he had been offered the promotion and that he had made the decision to quit after “careful consideration".
Mr Cain was said to be aggrieved over the appointment of Allegra Stratton, the former TV journalist brought in to host televised No 10 news conferences from next year, and feared being sidelined.
Amid concerns over her new role, he was offered the powerful role of chief of staff, which would have meant he was one of just a handful of people in No 10 with direct one-to-one access to Mr Johnson.
But the move was seen as entrenching the grip of the Vote Leave faction on the Downing Street operation and ran into immediate resistance, with Mr Johnson’s fiancee Carrie Symonds – who has clashed in the past with Mr Cummings – reportedly strongly opposed to the appointment.
Ms Stratton was also said to have objected to the appointment.
What does his resignation mean?
In Westminster, there are always rumours of rifts and rows and speculation about who is on the way up and who is going down. But this is all playing out at a time when the country is in the grip of coronavirus, with the official death toll passing 50,000 and the true figure far higher.
The public might reasonably expect that at this moment of crisis those involved in running the country should be more focused on that than internal squabbling at the heart of government.
The latest manoeuvrings come amid growing unhappiness among increasing numbers of Conservative MPs at the performance of No 10 and its handling of the coronavirus outbreak.
Sir Geoffrey Clifton-Brown, a senior member of the influential Tory backbench 1922 Committee, said Mr Johnson needed someone who could act as a link with the party in Parliament.
“I think it is essential for the Prime Minister to have a chief of staff. Somebody we can get hold of if we really need to,” he said.
Former Tory minister Jake Berry said the Prime Minister was “stamping his Johnsonian authority” on Downing Street.
The MP for Rossendale and Darwen told ITV’s Good Morning Britain: “The departure of Lee Cain does show, I think, that the Prime Minister is taking back control of his government.
“He’s moving from a campaigning operation to an operation solely focused on good government. I think it’s a good move for the Prime Minister.
“As we go past that grim milestone, as you say, of 50,000 deaths from this appalling disease, it’s high time, I think, that there was a bit of a change of guard in Number 10."Mr Cain is the latest in a series of Government resignations.
Who else has resigned under Boris Johnson?
Jonathan Slater, the permanent secretary at the Department for Education, 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 announced his departure from the role of Cabinet Secretary in June amid reports of clashes with Mr Cummings.
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”.
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.
In February this year, the top civil servant at the Home Office, Sir Philip Rutnam, resigned, accusing Home Secretary Priti Patel of bullying.
Sir Jonathan Jones reportedly left the Attorney General’s office on September due to a dispute with Downing Street over concerns the Prime Minister wanted to row back on parts of the Brexit deal relating to Northern Ireland.
There is no fixed date yet for the start of televised news conferences that Number 10 is planning, but Mr Johnson hopes they will help improve the Government’s public image.
The post-Brexit trade talks are entering their end game, with a resolution needed shortly if a deal is to be implemented by the time transition arrangements expire at the end of the year, when the UK leaves the single market and customs union.
The weakened position of the Vote Leave contingent within Number 10 could make it easier for Mr Johnson to compromise, although he has repeatedly insisted he is prepared to walk away without a deal.