FIFTY Shades of Grey has sparked a "revolution" in women's reading habits according to the romance literature giants Mills & Boon, and the subsequent surge in sales has prompted them to re-release some of their most erotic works.

The publisher is re-printing a series of "romances with a sinful edge" under the collected name 12 Shades of Surrender to cash in on the extraordinary success of EL James's trilogy.

Since Fifty Shades was re-released by Random House subsidiary Vintage Books in April, sales of Mills & Boon noted a 40 per cent rise in sales of digital romance books.

Kimberley Young, Mills & Boon's editorial director, said: "Fifty Shades has revolutionised book buying and how comfortable women have become reading and talking about this kind of book.

"Women's tastes have changed.

"They are much more open about sex and willing to discuss their fantasies."

The company set up its Spice subsidiary to publish more erotic material in 2008 and the advent of the Kindle has boosted sales.

"We've seen a rise in erotica over the past four years in the digital market," Ms Young said.