Booksellers are bracing themselves for blockbuster sales of a book tipped as the biggest publishing event since JK Rowling’s Harry Potter and the Deathly Hallows two years ago.

Pre-orders for The Lost Symbol, Dan Brown’s follow-up to The Da Vinci Code, have already made it’s sixth biggest-selling book of 2009. It has a first print run of 6.5 million copies, the largest first print in the history of publisher Random House worldwide.

Asda marketing manager for books Dewi Williams said: “We expect to sell just under 20,000 copies in the coming week, and customers and colleagues alike are gearing up for one of our biggest book-selling weeks of the year.”

Waterstone’s Piccadilly opened at 7am - two hours early - to sell the only signed copies of the UK edition of the £18.99 hardback. That price is likely to be heavily discounted in a price war that has already seen Asda reduce it to £5.

A spokesman for Waterstone’s said: “The book is destined to become the biggest selling adult fiction hardback of the decade.”