Harry Potter and the Half-Blood Prince is expected to be the biggest and fastest selling book in history. Waterstone’s expects to sell more than two million copies in the UK and ten million worldwide.

The first five Harry Potter books have sold more than 265 million copies in 200 countries and have been translated into 62 languages, helping to make J.K. Rowling, the author, Britain’s richest woman.

Such is the demand for a peek at the latest Harry Potter book that two men brandishing a replica gun tried to sell stolen copies to a reporter on The Sun for £50,000.

Barry Cunningham, who signed Ms Rowling to Bloomsbury, the publisher, said: “The success of Harry Potter is down to children’s own enthusiasm.”

However, Waterstone’s forecasts that more than 250,000 adults will purchase the adult-cover edition of Harry Potter and the Half-Blood Prince on its first day of release — which would make it the fastest-selling adult hardback book in history.

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