Fifty Shades of Grey author EL James on erotica book boom
19 April 2012 Last updated at 10:39 BST
The Fifty Shades of Grey series, by the British writer EL James, began as an e-book on a small print on demand website but has become a publishing phenomenon - topping the fiction chart.
The erotic romance author, who says she was inspired by Stephenie Meyer's Twilight series, told Newsnight she was "completely stunned" by the popular reaction to her books.
James says that it was popular in the UK and the US because "fundamentally, at its core, it's a love story".