Lawyers have conjured up a court order to stop details from the next Harry Potter book being revealed ahead of its official release, after several copies were sold by accident in Canada ahead of its official publication date on Saturday.

Raincoast Books, which is distributing Harry Potter and the Half Blood Prince in Canada, was granted a "John Doe injunction" by the British Columbia Supreme Court, preventing the buyers from revealing aspects of the novel’s plot.

Such information could prove valuable ahead of the book's release. Online bookmakers have been taking bets on just which leading character will perish in the sixth installment of JK Rowling's hugely successful series.

Police were reportedly involved in investigating suspicious betting patterns, which publishers feared suggested complex security measures had been breached.

The franchise has been lucrative for JK Rowling, the author of the Harry Potter books. She increased her wealth again this year, from an estimated £435 million in 2004 to £500 million, according to the Sunday Times Rich List.

Potter fans and Raincoast staff are now scouring the internet in case details from The Half Blood Prince are made available online, after around 15 copies were bought from a bookshop near Vancouver.

It is though that at least one copy had been offered for sale on eBay, the internet auction site, but was withdrawn when Ms Rowling's agents became involved.

Raincoast said: "It is not the intention of Raincoast to penalise the small group of fans who have innocently purchased a book in good faith.

"We look to them to ensure that the excitement and mystery of the story is preserved for fans around the world until July 16 by co-operating with us."

The court ordered all the copies be returned to the distributor, which has offered autographs from Ms Rowling, the book’s billionaire author, as a reward.

A Raincoast spokesman said some of the purchasers had already voluntarily returned their copies. But commentators have criticised the court for being heavy-handed.

Michael Geist, who holds the Canada Research Chair in Internet and E-commerce Law at the University of Ottawa, said: "People have legitimately purchased the book, yet now face violation of a court order if they fail to return it immediately, discuss it, or do anything else with the book.

"Why the court would grant such a broad order that reaches down to the underlying purchasers?" he asked, suggesting it could lead the way to "a real horror story".

The Half Blood Prince will have endured an eventful journey by the time the 11 million copies already printed reach the public.

A British newspaper reporter has already claimed that he was shot at in an attempt to recover the book and return it to its publishers in the UK, after an advance copy was allegedly offered for sale.

However, despite the unprecedented security operation mounted around successive Potter releases, previous instalments have also slipped through the net. In 2003, a Wal-Mart store in Quebec accidentally sold copies of Harry Potter and the Order of the Phoenix before the release date.

Times Recommends

• Darling under pressure on record public debt
• Mortgage drought deepens on 32% lending fall
• Oil prices firm after 10% drop to below $130