Boris Johnson’s memoir, which is published next week, is already topping the Amazon UK Books Best Sellers list, outselling recently published novels by Sally Rooney and Richard Osman.

Unleashed covers the politician’s career, from mayor of London to foreign secretary to prime minister. “Johnson’s book gives his version of the big episodes. But it dodges the larger issues they raise”, wrote Martin Kettle in his review of Unleashed. “Perhaps this overhyped book is the only memoir of which Johnson is capable. He is not going to change.”

The book has made headlines this week over its claims that the risk to peace in Northern Ireland from Brexit was exaggerated and was used by opponents “to trap the UK in the EU”, the revelation that many of Johnson’s family members urged him to back remain, and Johnson’s insistence he would have won the July election.

Unleashed has been hotly anticipated ever since it was revealed that Johnson had received an advance of about £510,000 to write it – although this figure is not as high as the sum that David Cameron was said to have received ahead of publishing For the Record in 2019 (£800,000) or the £4.6m advance that Tony Blair got for his 2010 autobiography A Journey.

Johnson’s memoir is priced at £30 (with a signed limited edition version available for £100), but Amazon is currently selling it for £15. The retailer’s “Best Sellers in Books” page ranks the books that are currently the most popular with its customers. It is separate from the Amazon Charts, which are updated weekly and list the Top 20 most sold and read books across the last seven days in nonfiction and fiction. In that chart, Unleashed is currently placed at number three in the nonfiction category, after Simply Jamie by Jamie Oliver and Unruly by David Mitchell.

Specific preorder information from other retailers is not currently available, but Kate Skipper, chief operating officer at Waterstones has confirmed that there have been “a considerable number of preorders” of Unleashed, “with numbers continuing to surge over the last few days as we near publication next week.”

“We have also seen huge interest in our upcoming event for Boris Johnson in conversation with Gyles Brandreth talking about his memoir at Manchester’s Bridgewater Hall later this month”, she added. That event will set attenders back £45, while a ticket to see Johnson at the Cheltenham literature festival costs £50. Tickets to both events include a signed copy of Unleashed.

Official first week sales figures (which will include preorders) will be released next week, and Johnson will have to shift more than 21,000 copies if he wants to improve on the first week sales of Cameron’s memoir and 92,000 to beat Blair. Liz Truss’s Ten Years to Save the West only sold 2,228 copies in its first week on sale earlier this year, but Johnson would be lucky to beat her record on a copies-sold-per-day-in-Downing-Street basis.

Johnson has previously written a number of books, including The Churchill Factor about his political idol, published while he was mayor of London. He was also paid an £88,000 advance in 2015 for a book about William Shakespeare, which was put on hold when he became foreign secretary and is still yet to be published.

• Unleashed by Boris Johnson (HarperCollins Publishers, £30). To support the Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply.