Boris Johnson’s communications director Lee Cain has dramatically resigned amid signs of a bitter Downing Street power struggle.
In a statement the former journalist said that after “careful consideration” he had decided to leave No 10 at the end of the year.
The shock move comes less than 24 hours after it was reported that he was to be promoted to the key position of the prime minister’s chief of staff.
Mr Cain was a close ally of Dominic Cummings, Mr Johnson’s chief adviser, having worked with him on the Brexit campaign.
The appointment was seen as consolidating the former Vote Leave team’s grip at the top of Downing Street.
However it provoked an immediate backlash with Mr Johnson’s fiancee Carrie Symonds reportedly opposed to the move.
ITV News Political Editor reported that Mr Cain felt sidelined by the PM's appointment of former ITV News National Editor Allegra Stratton as a spokesperson to deliver televised briefings.
Ms Stratton is reported to have wanted to report directly to Mr Johnson, something which Mr Cain felt was akin to a demotion for him, which ultimately resulted in his resignation.
Building on what Robert Peston has learnt, ITV News Political Correspondent Paul Brand said he understands that Mr Cain offered his resignation last week and "one version of events is that he was then offered the position of chief of staff by Boris Johnson.
"That then caused a backlash among others in Number 10, a huge power struggle then ensued and in the end it was the likes of Boris Johnson's fiancée Carrie Symonds who pushed back and said: 'No, we want Lee Cain to go.'
"Tonight he has decided that he will resign and instead the prime minister's spokesman, James Slack, will now take on the role of director of communications.
"All of this has created a whole lot of bad blood.
"There are lot of loyalists, loyal to Lee Cain who worked with him on Vote Leave.
"The whole of Number 10 tonight is embroiled in this huge toxic split and at a time when all of those figures should be fighting the virus there is a sense they're all too busy fighting one another."
In a statement announcing his resignation, Mr Cain said he was leaving despite having been offered the chief of staff post.
“After careful consideration I have this evening resigned as No 10 director of communications and will leave the post at the end of the year,” he said.
“It has been a privilege to work as an adviser for Mr Johnson for the last three years – being part of a team that helped him win the Tory leadership contest, secure the largest Conservative majority for three decades – and it was an honour to be asked to serve as the Prime Minister’s chief of staff.
“I would like to thank all the team at No 10 – including the many unsung and incredibly talented civil servants – for their hard work and support during the last 18 months.
“And most of all I would like to thank the Prime Minister for his loyalty and leadership.”
In response, Mr Johnson paid tribute to Mr Cain’s “extraordinary service” to the government over the past four years.
“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,” he said.
“He will be much missed.”
After the 2016 referendum, Mr Cain joined Mr Johnson as a special adviser when he was made foreign secretary by Theresa May.
He stuck with Mr Johnson when he quit two years later over Mrs May’s proposed Brexit deal and worked on his campaign to succeed her as Tory leader.
Former Tory Cabinet minister, Ken Clarke told ITV News Political Editor Robert Peston: "[Mr Cummings] is obviously exercising too powerful a role in the government, which is certainly agreed upon by quite a large number of the people I know, including quite a few who are holding senior posts in government."
Speaking on ITV's Peston programme, Lord Clarke said: "It does sometimes seem to me that all the key decisions are being taken are people who are more worried about tomorrow’s headlines."
In a statement, Labour accused the government of "fighting like rats in a sack".
“On the day the UK became the first country in Europe to report 50,000 coronavirus deaths and the public endure another lockdown, Boris Johnson’s government is fighting like rats in a sack over who gets what job," a Labour spokesperson said.
“It is precisely this lack of focus and rank incompetence that has held Britain back.
"The public deserve better than this incompetent and divided Conservative government.”