Boris Johnson insists he would have won July election in new book | Boris Johnson

Boris Johnson has insisted he would have won another election if he had not been forced from Downing Street, arguing in his new memoir that he broke no rules with lockdown parties and was the victim of a conspiracy.

The former prime minister’s book, Unleashed, also reveals that he believed the risk to peace in Northern Ireland from Brexit was exaggerated and was used by opponents “to trap the UK in the EU”.

Settling scores with a number of Conservative former colleagues, he calls David Cameron’s departure as PM immediately after the Brexit vote a “flouncerama” and details his sadness and anger when Michael Gove stood against him to be Tory leader in 2016.

What is likely to be the most controversial part of the book comes near the end, where Johnson writes about the revelations over lockdown-breaking No 10 parties, one of a string of controversies that forced him from office in July 2022.

Johnson was among more than 100 people fined for breaching restrictions in Downing Street, but in the book he writes: “At the time we believed that these events were in accordance with the rules – and I still think they were.”

His only mistakes, he adds, were “grovelling” in response and allowing a “ridiculous and unfair witch-hunt” – a reference to the report on Partygate led by Sue Gray, then a senior civil servant.

Johnson’s departure, amid a series of resignations from his government, was nothing more than the product of “a media-driven campaign being fed by some former advisers”, he writes, referring to Dominic Cummings, his former chief aide, and Lee Cain, who was his head of communications.

This condemned the Conservatives to defeat in the 2024 election, he argues: “So yes: if you ask me the counterfactual question, would I have won again if the Tories had kept me on, the answer is yes, absolutely.”

Another section of the 733-page book deals with the Brexit period, including the deadlock between 2016 and his election victory in 2019, something he blames in part on worries about a resurgence in IRA violence in Northern Ireland if border arrangements changed.

In the months after the Brexit vote, “the establishment in Britain combined with the EU to try and make a nonsense of Brexit and make it impossible to deliver”, he writes.

Discussing talks with the EU and European leaders over a planned withdrawal agreement in August 2019, shortly after he took over in No 10, Johnson claims they used Northern Ireland as an excuse to hold things up further.

“They wanted to rope-a-dope us, to see how long I could last,” he writes. “They were in an immensely strong position and they knew it.

“They had managed electrically to cross-wire the ambition of Brexit with the cause of peace in Northern Ireland, and anyone who disagreed with them – anyone who wanted to take the whole of the UK out of the EU – was at risk of being electrocuted, pssssscht, on a charge (however exaggerated) of putting that Northern Irish peace at risk.”

The book goes on: “It was that fear – let us be blunt, the fear of renewed IRA activity – that was being used to trap the UK in the EU. The argument was that once the UK had left, there would be a new land border with the EU, along the border between Northern Ireland and the republic.”

In another section of the book, about the buildup to the EU referendum, Johnson reveals that before he publicly supported a leave vote, his father and all his siblings urged him to back remain, although his then wife, Marina Wheeler, was “inclining towards leave”.

Describing the referendum campaign, Johnson accepts that the claim of a £350m-a-week outlay, as displayed on the side of the Vote Leave bus, was in fact nearer £175m when treated as a net amount, while adding: “That was still a hell of a lot of money.”

The remain campaign, in endlessly criticising the slogan, “made the cardinal mistake, in any campaign, of playing on our turf”, he writes.

Immediately after the referendum, Cameron announced he was resigning as prime minister, something Johnson criticises heavily. Describing Cameron’s departure statement in Downing Street, he writes: “He was walking back inside the black door and whistling some jaunty air, as though to say to us, the victors – right, you tossers, you’ve made this mess. Now you sort it out.

“I thought it was the wrong thing to do, and a bit petulant. Plenty of other European leaders sustain referendum defeats and carry on with their duties.”