'Fifty Shades Of Grey' has passed a new milestone to become the biggest-selling British novel for adult audiences.
Sales of the book -- which shifted another 660,000-plus copies last week -- overtook Mark Haddon's 'The Curious Incident Of The Dog In The Night-time', as a movie version came a step closer.
Producers of Oscar-winning The 'Social Network' have been announced as the team who will bring the film version of the erotic tale to the screen.
'Fifty Shades' -- the first of a trilogy of steamy tales, dubbed "mummy porn", by author EL James (pictured left) has become a literary phenomenon.
In the past week it sold 664,478 copies in paperback, bringing its total to 2.3 million since it was published in April.
In the past few days it surpassed 'Curious Incident', which has sold 2,160,000, and is now the 14th biggest seller since accurate records began in 1998.
The books which have outsold it have either been aimed primarily at younger readers -- such as the Harry Potter tales -- or are by overseas writers, such as Stieg Larsson and Dan Brown. Mr Brown's 'The Da Vinci Code' is the biggest seller in the UK.
'Fifty Shades' is only around 10,000 copies behind both Mr Brown's 'The Lost Symbol' and Stephenie Meyer's 'Twilight', so with Ms James's astonishing sales it will surpass them in a matter of hours.
Sales of her trilogy in the last week alone amounted to 1.4 million -- almost twice as many as the sales of the next 1,000 best-selling paperback novels combined, according to publishing industry magazine 'The Bookseller'.
The second book in the series, 'Fifty Shades Darker', sold 407,927 copies in paperback last week, while the third, 'Fifty Shades Freed', sold 369,477.