Boris Johnson’s senior adviser Dominic Cummings is expected to leave his position by the end of the year.
Mr Cummings told the BBC “rumours of me threatening to resign are invented”, after speculation this week.
But he added that his “position hasn’t changed since my January blog” when he said that he wanted to make himself “largely redundant” by the end of 2020.
And a senior Downing Street source said that Mr Cummings would be “out of government” by Christmas.
BBC political editor Laura Kuenssberg said there was no question the announcement of his departure was “accelerated by turmoil in No 10 in recent days”.
It comes after Lee Cain – the director of communications and an ally of Mr Cummings – stood down amid reports of internal tensions at Downing Street.
The pair are long-time colleagues, having worked together on the Leave campaign during the EU referendum – and Mr Cain’s departure prompted rumours that his ally would also step down.
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Speaking to the BBC’s political editor, Mr Cummings denied that he had threatened to resign after Mr Cain’s departure – and instead pointed out that he had indicated his own plans nearly a year ago.