Fifty Shades of Grey, by the little-known author EL James has topped the New York Times best-seller list.

A limited print run of the book, the first trilogy, has been cleared off bookshelves. However, the majority of sales were of e-books.

The series of books follows the steamy romance between “successful young entrepreneur” Christian Grey and “unworldly, innocent” literature student Anastasia Steele.

The small virtual publishing house, Australia-based The Writer’s Coffee House, has sold more than 250,000 copies.

James, the author, is a TV executive from west London. Also a mother of two, she has now signed a book deal in the US with global publisher Random House.

Her agent Val Hoskins said James was “overwhelmed” by the success.

She described the trilogy as a “21st century word-of-mouth hit”.

The three have been released today as an e-book by Random House offprint Vintage Books, and 750,000 paperback editions have been ordered.

James, whose full name has not been disclosed, said Fifty Shades of Grey had taken her on “an extraordinary and wholly unexpected adventure”.

She said she owes the popularity of the book to social networking, “both through social media websites, like Facebook, and friends talking to one another.”

Julia Bosman from the New York Times credited the books with “introducing women who usually read run-of-the-mill literary or commercial fiction to graphic, heavy-breathing erotica.”