Boris Johnson was toppled as prime minister after his close aides briefed the media that some staff in Downing Street had breached Covid rules during social gatherings to trap him into ‘lying’ about it, according to a new book.

Former No 10 adviser Dominic Cummings is said to have hatched the plot as retaliation for alleged briefing against him and his colleagues by Mr Johnson’s wife Carrie.

He is then said to have constructed an elaborate plan to lure the then-prime minister into denying the Covid breaches and lighting the fuse towards his downfall.

The claims, detailed in Out by political writer Tim Shipman, appear to confirm Mr Johnson’s insistence that he was the victim of a ‘political assassination’ by Mr Cummings and his allies.

The book, extracts of which were published in the Sunday Times, traces the origins of the plot back to a conversation between Mr Johnson and Mr Cummings in November 2020, when Mr Cummings confronted the then-PM over claims Mrs Johnson and her allies were briefing against him.

He is said to have told Mr Johnson: ‘You’d better get a grip on that, or things are going to blow up out of your control. When we leave, your girlfriend is going to say a bunch of s*** and I’m going to hold you personally responsible for what she says. You know what that means for you, don’t you?’

After Mr Johnson asked if he was threatening him, Mr Cummings replied: ‘Yes, I’m f***ing threatening you.’

The following October, Mr Cummings was called by an ally who said that ‘a lovely golden nugget is falling into our laps’.

It was footage from a mock press conference at the height of the second Covid lockdown showing Allegra Stratton, the prime minister’s press secretary, joking about Downing Street parties.

Mr Cummings and his allies then briefed the story to the Daily Mirror, starting the chain of events which led to Mr Johnson being investigated by the police and senior civil servant Sue Gray and accused of lying to the Commons about whether Covid rules had been broken.

Mr Cummings is reported to have said: ‘We could trap the f***er into lying about it. He’ll just tell everyone to just deny it all.’

After Mr Johnson repeatedly insisted that ‘all guidance was followed’, Mr Cummings is said to have replied: ‘When the truth drips out, it’s going to break him.’

The furore contributed to the political pressure on Mr Johnson which led to his resignation as prime minister in 2022.

Last night former Cabinet minister Nadine Dorries, a close ally of Mr Johnson who wrote about Mr Cummings’ role in bringing down Mr Johnson last year in her bestselling book The Plot, said: ‘This is Cummings’ version of events. Boris never knowingly lied to Parliament or to anyone else. He was a prime minister doing his job, depending on those who were running Downing Street and the Cabinet Office, people like Sue Gray and others, to keep him informed of what had taken place.

‘He was lied to by those whose job it was to provide the facts and to protect the integrity of the Government. This is exactly what I revealed in The Plot which was disputed by Cummings’.