An erotic book dubbed as "mummy porn" has beaten the J K Rowling authored Harry Potter's record in the UK book sales chart, becoming fastest selling paperback of all time in just one week.
The book "Fifty Shades of Grey," about a depraved relationship between a young female virgin and her rich older lover has become the fastest selling paperback since records began.
Erika Mitchell, who writes with the pen name 'EL James' beat JK Rowling and Da Vinci Code author Dan Brown in the UK records with the first instalment of her X-rated trilogy, the Daily Mail reported.
The first instalment of the X-rated trilogy, sold more than 100,000 paperback copies last week alone a success story which most of the Harry Potter books and all of the Twilight novels have failed to match.
At first, most sales of 'The Fifty Shades' series were of the more discreet e-book version, as the trilogy's popularity soared its sales have taken off.
The book has been Britain's best-seller for the past nine weeks, as the three book series held the top three spots on the UK charts for the past six weeks.
Experts say the success of the racy books, dubbed- "mummy porn"- has been driven by frustrated middle-aged mothers.
"The success has not been driven by people who regularly buy books, but by people who buy maybe three or four books a year," spokesman for Nielsen Book-Scan, who complies the official chart figures, said.
"The books have crossed into the mass market. Clearly, people aren't embarrassed by it anymore," the spokesman said.
Philip Stone, who compiles book charts for The Bookseller magazine, said their reputation had been spread 'totally through word of mouth'.
"It is highly unusual for a book to sell so well without there being a film adaptation or the author being well known, like Dan Brown or JK Rowling," he said.
Erika, 49, initially posted the tales on the Internet as fan fiction based on the Twilight books.
Two years later, she is said to be worth almost 4 million Euros after signing book deals on both sides of the Atlantic and a Hollywood movie contract a few months ago.
The Fifty Shades trilogy tells of the sexual awakening of university student Anastasia Steele and her relationship with handsome billionaire Christian Grey.
While there are a number of graphic sex scenes, some involving sado-masochism, it is centred on a conventional love story.