50 Shades of Grey surpasses Harry Potter to become Amazon's all time best seller

The mummy porn hit about the sexual exploits of Anastasia Steele has sold more than 4 million copies sold in four months.

JK Rowling's Harry Potter and the Deathly Hallows was the previous title to hold the record, but EL James's novel has outsold it more than two 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," said Gordon Willoughby, from Amazon.

"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.

British author James's erotic trilogy is set to become a film, with Scarlett Johansson and Kristen Stewart, rumoured to take on the roll of Steele.

Scientists have even got in on the act, rendering the novel's BDSM love interest, the billionaire, Christian Grey's face.

The novel has gone on to inspire a plethora of copycats including Kiwi version, 'Eighty days Yellow,' a novel which contains the words 'pelvic assault'. Sexy.