Boris Johnson could be paid more than £1m for his memoir, according to publishing insiders. But anyone expecting a kiss-and-tell may be disappointed, as industry professionals have said he is unlikely to open up about his personal relationships.

A publisher, who wished to remain anonymous, told the Guardian that while it was “way too early for anything concrete to happen or be submitted”, they would “be amazed if he doesn’t sign up somewhere for memoirs at some point in the autumn”.

Martin Redfern, executive director and literary agent at Northbank Talent, told trade magazine the Bookseller that he thought the book would command “north of £1m”.

However, he did not think Johnson would “change the habit of a lifetime and divulge details of his colourful private life”.

Johnson announced last week that he was stepping down as Conservative party leader, and a fierce contest is under way to appoint his successor.

There has been speculation that Johnson, who worked as a journalist before becoming prime minister, could return to writing, publishing a book about his time leading the country and earning a large sum from it.

One literary agent said they thought “for a memoir like his, it would be a high six-figure or even a seven-figure deal”, with the serial rights, in particular, being “very lucrative”.

The agent said that although Johnson was a divisive figure, they thought the memoir would sell well, adding: “I think it would be popular because of how controversial he is: people would read it even just out of curiosity.”

It is not known when a Johnson memoir might be announced, but one of publishing’s biggest trade fairs, the Frankfurt book fair, is coming up in the autumn. Many agents and publishers wait until close to the event to announce big books, in the hopes of drumming up more excitement.

Recent prime ministers are all thought to have earned sums of six figures or more for their memoirs. David Cameron’s For the Record was sold in a “hotly contested and significant” deal, while Gordon Brown’s My Life, Our Times was sold for an “undisclosed sum”.

Tony Blair’s A Journey was reportedly sold for an advance of about £4.6m, although all the money he made was donated to the Royal British Legion.

Other than Blair, Johnson is arguably the most famous British prime minister of recent times internationally, and agents have predicted interest from beyond the UK should he write a memoir.

Juliet Mabey, publisher at independent Oneworld, told the Bookseller she thought “quite a few” UK and US publishers would be interested in Johnson’s memoir.

Johnson had a long career as a journalist before becoming prime minister, working as editor of the Spectator from 1999 to 2005 and as a columnist for the Telegraph. His previously published books include The Churchill Factor, a bestseller published in 2014 that looked at the career and success of Winston Churchill.

Johnson was also due to write a book about Shakespeare, for which he was reportedly paid £500,000 in a deal he signed in 2015 with the publisher Hodder & Stoughton.

Shakespeare: The Riddle of Genius remains undelivered. In 2019, Johnson said being prime minister meant he would not “be able to rapidly complete a book on Shakespeare that [he had] in preparation”.