Dominic Cummings will leave No 10 by Christmas it has emerged, plunging Boris Johnson's under fire Downing Street deeper into chaos.
Mr Cummings signalled he will leave No10 by the end of the year – suggesting he had planned at the start of this 2020 to be gone by Christmas.
He told the BBC: “My position hasn't changed since my January blog.”
That referred to a piece he posted online 10 months ago when he wrote about transforming Whitehall, adding: “We want to improve performance and make me much less important — and within a year largely redundant.”
The BBC also quoted a Downing Street source as saying Mr Cummings would be "out of Government" by Christmas.
Mr Cummings opponents - in Labour and the Tories welcomed the departure of the controversial advisor.
Deputy Labour leader Angela Rayner tweeted: “I have no interest in Dominic Cummings’ apparent ‘legacy’.
"In the middle of a pandemic he shattered public trust and undermined lockdown & our fight against Covid.
"His cross-country road trip, long distance eye test, dishonesty & arrogance was an insult to the British people.”
Her colleague, Shadow Health Secretary Jonathan Ashworth, posted: “NHS staff are working under immense Covid pressures.
"Beds are filling up with ill patients. Relatives with a loved one in a care home are desperate to see their relations.
"And Downing Street is paralysed by the soap opera of these self indulgent spin doctors. It’s pathetic.”
Senior Conservative backbencher Sir Bernard Jenkin said he is not surprised that Dominic Cummings is leaving, adding: “Nobody is indispensable.”
The chairman of the Commons Liaison Committee said: “It’s an opportunity to reset how the Government operates and to emphasise some values about what we want to project as a Conservative Party in Government.
“I would suggest there are three words that need to become the watch words in Downing Street – they are respect, integrity and trust.
“Certainly in the relationship between the Downing Street machine and the parliamentary party there’s been a very strong sense that has been lacking in recent months."
It comes after one of the PM's closest aides, Lee Cain, quit amid a bitter internal power struggle.
Cain, No10's Director of Communication, quit on Wednesday night following a row over the Chief-of-staff position.
Mr Cummings and Mr Cain are close political allies, having worked together since the Brexit campaign. Mr Cummings was said to be unhappy with the way his friend had been treated.
Boris Johnson reportedly talked Cummings out of resigning immediately following Cain's resignation - but he has since told the PM he will leave by Christmas.
Reports claim Cummings put forward another ally, Cleo Watson, for the top role but Boris Johnson refused to offer her the job.
The pair then agreed that Cummings should leave ad it's believed he will vacate No10 by December 31 - the end of the Brexit transition period.
The Telegraph reported an "associate" of Mr Cain as saying the communication chief's departure was the "beginning of the end for Dom".
"Lee is the person who has been covering Dom's flank 24 hours a day and he will soon be gone," the source told the paper.
A source told the Daily Mail that the loss of Cain "will loosen Dom’s grip on government and hasten his departure".
"He wants to get Brexit over the line, get over the hump of the pandemic and get one or two of his pet projects locked in. Once that is done, he won’t hang around."
Others who could potentially follow the pair include chief Brexit negotiator David Frost.
But sources also told the Mail that while Lord Frost, along with Cummings, was unhappy with Cain's departure, he would remain in his position.
Conservative MPs have urged Mr Johnson to use events to reshape the team inside Downing Street and reconnect with the parliamentary party, some of whom feel he has been "lost" to advisers over the past year.
Mr Starmer described No10 as "pathetic", telling LBC: “Pull yourselves together, focus on the job in hand.”
In his resignation statement, Mr Cain confirmed he had been offered a promotion to the key position of the Prime Minister’s chief of staff.
The move – 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 – was seen as entrenching the grip of the Vote Leave faction on the Downing Street operation.
However it 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.
Allegra Stratton, the former TV journalist brought in to host televised No 10 news conferences from next year, was also said to have objected to the appointment.
It's reported that Cain was worried he'd be side-lined by Ms Stratton's US-style media briefings and offered to resign last week.
However, the PM didn't want to see him go and so offered him the vacant Chief-of-Staff role.
Mr Cummings was in favour of the promotion but it sparked fury among senior Tories who feared it would further embolden the Vote Leave faction in No10.
Ms Symonds then went on to tell the PM it was "mistake" to appoint Cain to the role.
However, news of the promotion and the ensuing row had already leaked and Mr Cain decided to resign.
In his resignation statement, Mr Cain – a former tabloid journalist – said he had decided to resign as communications director after “careful consideration”.
He said it had been an “honour” to have been offered the post of chief of staff and he thanked 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.”
It is expected that Mr Cain will be succeeded by James Slack, the Prime Minister’s official spokesman who also held the post under Theresa May.
Unlike Mr Cain who is a political special adviser, Mr Slack, a former Daily Mail journalist, is a member of the permanent Civil Service.
Mr Cain originally joined Mr Johnson when he was made foreign secretary by Mrs May following the 2016 Brexit referendum.
He stuck with Mr Johnson when he quit two years later over her proposed Brexit deal and worked on his campaign to succeed her as Tory leader.
If he is followed out of No 10 by Mr Cummings, there will be many in Westminster who will not be sorry to see him go.
As Mr Johnson’s top adviser – who was brought in when he became Prime Minister last year – Mr Cummings has been a pivotal figure in Downing Street.
However his abrasive manner and open contempt for MPs has earned him many enemies in Whitehall.
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 told the PA news agency.