Just days before the book's eagerly-awaited launch, police are investigating the theft of a copy of E.L. James's latest instalment in the Fifty Shades of Grey saga.

The prequel, Grey, retells the meeting of unworldly Anastasia Steele and the BDSM loving billionaire Christian Grey in his "own words, and through his thoughts, reflections and dreams".

It is feared thieves may leak the novel, or sell extracts on the blackmarket in advance of its planned publication on June 18th, Christian Grey's birthday.

Publisher Penguin Random House brought in police when it discovered a copy of the novel missing Monday in Kent, England. It's not known if the copy went missing during printing or distribution.

"Grey will be published on June 18th - Christian Grey's birthday - as planned," it said. "We can confirm that the Kent police are investigating the theft of a finished copy of EL James's new book Grey.  We will not be issuing any further statement."

It's not the first time prized manuscripts have been stolen.

In 2008 Stephenie Meyer abandoned a partially written novel Midnight Sun, which was to have been a fresh take on the Twilight series from the perspective of the vampire Edward Cullen, when it was stolen and posted on the internet.

Thousands of copies of the long-awaited fifth Harry Potter book were stolen from a warehouse just days before that book's launch.

The Fifty Shades of Grey trilogy has sold more than 125 million copies worldwide since the first book's initial release in 2011 on a fan-fiction website run out of Sydney.

The first book was turned into a Hollywood movie, released earlier this year, starring Jamie Dornan and Dakota Johnson.

Author James, whose real name is Erika Mitchell, had kept the new book a secret, only announcing it's imminent release on June 1.

On the opening page James dedicates Grey to "those readers who asked . . . and asked . . . and asked for this".

The cover blurb reads: "Christian Grey exercises control in all things; his world is neat, disciplined and utterly empty - until the day that Anastasia Steele falls into his office in a tangle of shapely limbs and tumbling brown hair.

"Unlike any woman he has known before, shy, unworldly Ana seems to see right through him - past the business prodigy and the penthouse lifestyle to Christian's cold wounded heart."

"Christian is a complex character and readers have always been fascinated by his desires and motivations, and his troubled past," she said in a statement.

"Also, as anyone who has ever been in a relationship knows, there are two sides to every story."

Meanwhile, a US court will decide next month how much the Sydney publisher of the Fifty Shades of Grey trilogy will be liable to payout her Texas partner.

The award is likely to run into millions.