Author EL James has sold almost a million paperback copies of her racy Fifty Shades trilogy in only a week, latest figures show.
Her first book Fifty Shades Of Grey has had its highest sales yet, shifting 482,785 copies to set a new UK record for the biggest weekly tally for a paperback book.
Global sales of the books by the west London-based writer have now shot past 20 million, just 12 weeks after it first hit UK bookshelves.
Figures from Nielsen Bookscan, which compiles sales data for the publishing industry, show the books sold 978,197 copies in a week as demand continues to grow.
Publishers have now had to order 17 reprints in the UK since it came out in just a quarter of a year, with printers having to work around the clock to cope with interest in the tales of "mummy porn".
James's debut novel, Fifty Shades of Grey, saw its sales rise by 21 per cent on the previous week, but its sequels clocked up massive sales. Second book Fifty Shades Darker shifted 264,984 copies and the final instalment, Fifty Shades Freed, rang up sales of 229,171.
The mum-of-two, whose real names is Erika Leonard - originally published her erotic tales as ebooks and her publishers say they continue to sell well digitally, estimating that they are largely matching print sales.
Publishing trade magazine The Bookseller today reported the first book has now sold 1,645,422 copies in just 12 weeks. Dan Brown's The Da Vinci Code - the biggest selling UK paperback of all time - took 46 weeks to reach that figure.
The magazine's website points out that STG4.7 million ($A7.22 million) was spent on James's books in a week and accounted for 40 per cent in every pound spent on a novel.
James's books have occupied the top three places in the best-seller lists for 10 consecutive weeks.
Fifty Shades of Grey has already become the first book to sell more than one million copies for Kindle.