It has sold over 70 million copies worldwide, with many fans calling it one of the best erotic romances they've read, but not everyone is enamoured with "Fifty Shades of Grey." Bestselling novelist Barbara Taylor Bradford has slammed fellow British author E.L. James' popular trilogy series, calling it "not even sexy."

Speaking to Radio Times, the veteran writer didn't hold back when she called the erotic novel as "terribly badly written, repetitive, and not even sexy."

"Fifty Shades of Grey" started as a fan fiction for another romance book "Twilight," which has since been adapted into a film series. In its first instalment, released in 2011, readers are introduced to the virginal college graduate Anastasia Steele who caught the eye of young billionaire Christian Grey. Their relationship quickly became sexual, with the book giving a lot of emphasis on their dominant-submissive relationship.

The second and third instalments, "Fifty Shades Darker" and "Fifty Shades Freed," continue their romantic and sexual relationship while Christian fights his own demons.

Although the critical reception of the series ranges from mixed to negative, it has enjoyed enormous commercial success. It has been dubbed as the book that has put "mummy porn" stories on spotlight, which therefore has opened the avenue for other erotic writers to publish their own work.

But Taylor Bradford, whose 1979 debut novel "A Woman of Substance" has sold over 30 million copies worldwide, James' book was simply awful.

"When the female character has her bottom smacked with a whip it's the end of the book, except her saying 'Holy cow!' [she mimics, sounding like a mewling cat] in excitement. The 'hero' is every woman's worst nightmare, in my opinion, although he's rich," she continued.

Taylor Bradford is one of the most recognisable names in literary fiction, and has written 27 bestselling novels. Some of books were adapted as a TV miniseries in the UK.

Though she has just slammed another successful woman's work, she ironically admitted that she herself is wary of jealous women.

"Some women can be a bit devious, especially if you're successful. They're jealous and envious, although they'd be afraid to display that with me. I'd punch them in the face."