Dan Brown's Inferno: Publishers poised for biggest-sales since Harry Potter as Da Vinci Code author's latest Robert Langdon story hits shelves

Dan Brown's new book, Inferno, is roundly expected to whoosh off the shelves - both wooden and digital - upon release tomorrow, its author having already shifted more than 200 million books worldwide.

Following on from 2009's The Lost Symbol, which sold half a million copies in hardback in its first week, Brown's latest book has already made its mark on sales patterns. It has already had the honour of dragging its Medieval namesake, the 14th Century Italian poem by Dante Alighieri, to the top of Waterstones' poetry bestseller list - whether because people are interested in the new novel's origin, or by mistake it is not quite clear.

The fourth in Brown's Robert Langdon series - which kicked off with The Da Vinci Code in 2003 and has since sold 80 million copies- has already received the largest level of customer pre-orders since JK Rowling's The Casual Vacancy at high street bookseller Waterstones.

The novel is already atop Amazon’s top-selling book list, beating all currently available tomes despite still not having been released. Its hardback and Kindle editions are also in both first and second place on Amazon's pre-order chart.

Chris White, Waterstones' fiction buyer, said: "This should be the fastest and biggest selling novel of the year – it's hard to see how anything could beat it. It'll be a huge hit now and throughout the summer, then see another peak at Christmas. It could well be No 1 on 25 December."

The chain's flagship London store will open at 8am tomorrow with 200 signed copies to sell to the first 200 customers.

Retailers are already in something of a price war with Tesco, Asda and Amazon are selling the book, which carries a £20 cover price, for £9. Waterstones is selling it online for £10.

Inferno has been shrouded in the kind of papal secrecy Robert Langdon battled against in some of his earlier outings, with translators kept for weeks in the high-security basement at the Milan headquarters of Mondadori, Italy's largest publishing firm, under strict confidentiality agreements, disallowed access to phones or notebooks. Security guards transported them in minibuses between their hotel and the bunker.

In his only newspaper review ahead of the release, Brown told The Sunday Times he hangs upside down to combat writer's block. He does so using a table by strapping himself to a table in his gym, and then rotates the table until he is hanging vertically upside down.

“It does help," he said. "You’ve just got to relax and let go. The more you do it the more you let go. And then soon it’s just, wow.”

He also promised that Inferno would be his "darkest novel yet," and somewhat mysteriously dangled the fact that there's a "huge piece that we’re not talking about, that is secret and timely, that is really what is going to be most controversial about the book."

“I’ve known for quite some time that I would write a book based on the Inferno. Having written Da Vinci Code and Angels and Demons, I’ve spent a lot of time on Christian ideology and history.

"The Bible states that there’s an underworld, and it hints that it might not be a very nice place, but it wasn’t until the 1300s and this vision of Inferno that it became terrifying. Dante has had enormous influence on the Christian view of hell.”

The Independent's first review of the book will be online at midnight tonight