Fifty Shades of Grey is now the best-selling book in the UK of all time, having sold more than 5.3 million copies, according to its publisher.
The book, the first in a trilogy of steamy tales dubbed ‘mummy porn’, has become a literary phenomenon.
Author EL James said: “My main ambition when I signed the deal with Random House was to see my books in the shops. I simply had no idea they would be so successful and this is totally unexpected.
“The whole process has been both extraordinary and rewarding. I couldn't be more pleased with the sales and would like to thank everyone involved.”
The second and third books in the trilogy, Fifty Shades Darker and Fifty Shades Freed, have sold around 3.6 million and 3.2 million copies respectively.
Susan Sandon, managing director of Cornerstone Publishing which is part of Random House, said: “The Fifty Shades of Grey phenomenon is perhaps one of the most extraordinary experiences of my entire publishing career and I feel privileged to be part of it.”
All three books are due to be filmed as part of a movie deal.