The novel also became the website's biggest-selling book of all time, eclipsing the sales of the previous record holder, "Harry Potter and the Deathly Hallows", by more than two books to one.

"If J.K. Rowling was the literary phenomenon of the last decade then E.L. James looks certain to take that mantle in the current decade," Gordon Willoughby, EU Director of Kindle, said in a statement.

"In just four months, E.L. James has become Amazon.co.uk's biggest-selling author of all time which is truly remarkable when you consider that we've been selling books for almost 14 years," he said.

Fifty Shades of Grey, James' first book, tells of the sadomasochistic affair between wealthy entrepreneur Christian Grey and naïve literature student Anastasia Steele.

Widely dubbed "mummy porn", the steamy novel topped book charts all over the world following its release in 2011, selling more than 4 million copies in print and on Kindle at Amazon's UK website alone since March 2012.

The x-rated book broke a separate British record in June when it became the fastest paperback to hit one million sales, taking 11 weeks to reach the mark.

Movie rights to the trilogy were bought up by Universal and Focus Features, U.S. media reported in March.

(Reporting by Alice Baghdjian; editing by Steve Addison)

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