Boris Johnson is counting the cost of a power struggle in No 10 which resulted in the resignation of one of his closest aides.

Lee Cain announced late on Wednesday that he was quitting as director of communications amid a bitter row in Downing Street.

He had been offered the post of chief of staff, but a backlash among Tories and the Prime Minister’s inner circle ultimately led to his departure from No 10 rather than a promotion.

His exit has sparked speculation that he could be followed by Dominic Cummings, Mr Johnson’s top adviser who is 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 that he had decided to stay on for now to work on the Government’s response to the coronavirus pandemic – in particular the acceleration of the mass testing programme.

Mr Cummings remained tight-lipped as he left his home on Thursday morning.

Mr Cain, who will stay in post until the end of the year, was spotted heading into No 10 clutching a coffee.

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.

Ms Symonds is a former Tory press chief who has served as a special adviser in previous governments.

Allegra Stratton, the former broadcaster brought in to host televised No 10 news conferences from next year, was also said to have objected to the appointment.

Ministers attempted to play down the chaos at the heart of government.

Communities Secretary Robert Jenrick told BBC Breakfast: “The Prime Minister runs the Government.

“He is surrounded by a good team, a strong team of advisers, and, of course, the Cabinet.

“Our sole focus in Government is trying to steer the country through the pandemic.”

Former minister Jake Berry 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.”

Labour leader Sir Keir Starmer told LBC Radio the Downing Street infighting is “pathetic”.

“We’re in the middle of a pandemic. We’re all worried about our health and families, we’re all worried about our jobs, and this lot are squabbling behind the door of No 10,” he said.

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 was 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.

The latest manoeuvrings come amid growing unhappiness among increasing numbers of Conservative MPs at the performance of No 10 and its handling of the Covid-19 outbreak.