An award-winning author has whipped up controversy by describing Catherine, the Duchess of Cambridge, as a "machine-made" doll with a "plastic smile" who lacks the personality and human frailty shown by Princess Diana.

Hilary Mantel, who has twice won the Man Booker Prize for her historical novels set in Tudor times, made the comments in a talk for the London Review of Books titled "Royal Bodies," looking at how royal lives play out under the public gaze.

The furor over her comments came as Catherine carried out her first official engagement since she announced her pregnancy, with a visit to an addiction treatment clinic in London.

While there, she told reporters it would be "unnatural" if she was not nervous about having a child.

The duchess, who is patron of the charity that runs the clinic, Action on Addiction, was briefly hospitalized late last year with acute morning sickness. She and husband Prince William are expecting a baby in July.

In her lecture, Mantel described how Catherine's public image was first defined by her clothes, and then her pregnancy.

Before she became a mother-to-be, "I saw Kate becoming a jointed doll on which certain rags are hung," Mantel said, and "a shop-window mannequin, with no personality of her own, entirely defined by what she wore." Now, she will be portrayed as "her only point and purpose being to give birth."

The author also suggested the chief attribute brought by Catherine to her royal marriage was good manners, adding that the duchess "appeared to have been designed by a committee and built by craftsmen, with a perfect plastic smile and the spindles of her limbs hand-turned and gloss-varnished."

And Mantel contrasted that with the potential for disaster that Diana, the late Princess of Wales and mother to princes William and Harry, carried with her, saying Kate was "irreproachable: as painfully thin as anyone could wish, without quirks, without oddities, without the risk of the emergence of character."

Unlike Diana, "whose human awkwardness and emotional incontinence showed in her every gesture," Mantel said, Kate appears to be "precision-made, machine-made."

In the first official portrait of the duchess, unveiled by artist Paul Emsley in January, her "eyes are dead" and she wears a strained smile, the author added.

Mantel was also critical of the public and the media, which, she suggests, place royal women under unhealthy scrutiny, particularly when it comes to producing a royal heir.

Nonetheless, her words attracted fierce criticism Tuesday.

Royal commentator Robert Jobson dismissed Mantel's remarks as "a cheap publicity stunt" and questioned whether she had ever met Catherine or seen her at work.

"People who meet Kate warm to her," he told CNN. "She has a winning smile and easy charm. Yes, she has a long way to go, and is not the new Princess Diana as many in the media are hoping for.

"But I think she is slowly but surely carving out a role for herself."

In the Telegraph newspaper, women's editor Emma Barnett branded Mantel's comments "not only unfounded, but incredibly cheap."

It is very early days for Kate as a royal, and her image is being carefully managed, Barnett said. "She has ample time to develop her public persona and become a fully-fledged role model if needs be," she said.

Nor does Catherine have the luxury of answering criticism, she added. "As a fully paid-up member of the royal family, she can only respond by doing the very same thing Mantel has criticized her for: staying quiet."

The Daily Mail also blasted Mantel's comments as "an astonishing and venomous attack."