The reality is rather different. The author of the "mummy porn'' book Fifty Shades of Grey is a middle-aged married woman living in a modest semi-detached red-brick house in a rather unfashionable area of west London.

While the heroine of her book, the virginal college girl Anastasia, eventually wins her damaged Prince Charming, the rich and handsome Christian Grey, a bondage-addicted billionaire, James is, in reality, a modest 49-year-old with the name of Erika Mitchell.

She lives near Ealing, with a husband she has been married to for some 20 years and two teenage sons.

Asked to describe what living with the new S&M queen of fiction was like, her husband, Niall Leonard, said : " Mostly it's just like being married."

His wife has confessed that Leonard rather tired of the experimentalism she used as primary research for the book and its two sequels.

She has said: "We have a very happy marriage. We annoy the hell out of each other, but generally we get on really well."

It is all a million miles away from her hero Christian's "red room of pain'' hidden in his penthouse. In Twitter chats, Mitchell has revealed that she drives a Mini and she loves eating Nutella with a spoon. Her husband snores, and she is not a morning person.

So will his wife's success change their low-key lifestyle? It seems sure to: Universal Pictures has bought the film rights to Fifty Shades for $5-million, with Scarlett Johansson or Angelina Jolie tipped as favourites to play the lead role. The book is being translated into 40 languages and is expected to lead to a "Fifty Shades baby boom" because it, apparently, awakens women's interest in sex.

So why has Mitchell been so publicity-averse? Her agent, Valerie Hoskins, said: "It seems she doesn't need to do interviews - the books are selling like hot cakes anyway."

And when asked if her sons had read the books, Mitchell was aghast: "No, good God no. I'd be mortified."

However, her mother and 82-year-old aunt have read the books, and apparently enjoyed them.