Boris Johnson's top adviser Dominic Cummings quits No 10 with immediate effect

Dominic Cummings has “decided to leave 10 Downing Street with immediate effect,” it was reported tonight.

Boris Johnson’s senior advisor had announced his intention to leave Downing Street.

But the controversial assistant to the prime minister was expected to step down by the end of the year.

Mr Cummings says he always intended to leave at the end of the year, but all signs are that he is leaving after a power struggle in the prime minister’s inner circle.

He wanted his closest ally Lee Cain – the No. 10 communications director – to be installed as Mr. Johnson’s chief of staff, strengthening his own hold on the Downing Street operation.

But the proposed move infuriated many senior Tories – and allegedly Carrie Symonds, the Prime Minister’s fiancée – who were troubled at the prospect of Mr. Cummings expanding his influence even further.

When it failed, Mr Cain – who feared he would be sidelined by the appointment of a new press secretary – announced that he would stop.

Mr. Cummings says the reports he threatened to resign on the spot are an “invention”, but he was clearly very unhappy with what happened.

In just over 24 hours, he told the BBC he was going too.

Mr. Cummings was considered more powerful than most of the ministers, who controlled the government’s agenda and demanded iron discipline from the army of Whitehall’s special advisers.

As a Vote Leave campaign leader, he is believed to be the mastermind behind the 2016 Brexit referendum vote and credited with playing a key role in last year’s overall election victory.

But his abrasive demeanor and open disregard for MPs and officials earned him many enemies in Westminster, who will not regret seeing him leave.

Some in Westminster predict it will lead to a less confrontational style of government with more focus on issues such as climate change and building bridges with the decentralized administrations.

Unhappy Tory MPs, who have felt ignored by No. 10 since the election, will hope that Downing Street will get them involved.

Others expect the government to be less likely to fight in a range of settings – from the BBC and the media to the judiciary.