Four people were today being questioned about the suspected theft of proof copies of the new Harry Potter book.

The arrests followed the reported discovery of two manuscripts of Harry Potter and the Order of the Phoenix in a field in Suffolk earlier this week, which were given to the Sun newspaper.

Suffolk police said they had arrested two 16-year-old boys and a 44-year-old man in Beccles, Suffolk, and an 18-year-old man in Harleston, Norfolk, late last night. They were held on suspicion of the theft of manuscripts from premises in Bungay and attempting to obtain property by deception.

Police said they had taken the four men to Lowestoft police station for questioning.

Amid intense anticipation of the release of the fifth book in the Harry Potter series, the publisher Bloomsbury is anxious to keep the plot secret until the official release of the book on June 21. It has imposed strict conditions on retailers regarding the storage of the book.

The Sun reported on Tuesday that a man walking his dog in Suffolk had found two copies of the book and handed them over to the newspaper, and that a third copy had been offered to the paper for £25,000. The paper says it refused the offer, and has put the other two copies under lock and key.

The book is being printed at Clays Ltd in Bungay, Suffolk, and the two copies were reportedly found nearby. Industry sources said they were probably "make readies" - early test-runs of the book, and probably incomplete.

Beccles, where three of the four were arrested, is about 10km away from the printing press.