A pregnant Kate Middleton has appeared for the first time with a noticeable baby bump, as the public backlash continues against a best-selling author who claimed Middleton's only purpose was breeding.

The Duchess of Cambridge appeared healthy on a visit to Hope House, an addiction recovery centre for women in Clapham, south London, late yesterday.

According to the Daily Mail, author Hilary Mantel's comments did not seem to faze Middleton.

Mantel, a double Booker Prize-winner, told academics at a lecture at the British Museum that Middleton was "machine-made" compared to Princess Diana.

"Kate seems to have been selected for her role of princess because she was irreproachable: As painfully thin as anyone could wish, without quirks, without oddities, without the risk of the emergence of character," said Mantel.

Her scathing comments made headlines around the world and have earned the ire of the public and British Prime Minister David Cameron.

The Mail reported he waded into the saga while on a trip to India.

He said Mantel was "a great writer" but described her comments on Middleton as "a hurtful thing to say".

Cameron told the BBC: "What I've seen of Princess Kate at public events, at the Olympics and elsewhere is someone who's bright, who's engaging, who's a fantastic ambassador for Britain.

"We should be proud of that, rather than make these rather misguided remarks."

Mantel went on, in her lecture, to describe Middleton as "bland" compared to Diana.

"She appears precision-made, machine-made, so different from Diana whose human awkwardness and emotional incontinence showed in her every gesture."

She said Middleton would become a "jointed doll on which certain rags are hung", as she would be only defined by what she wore.

"These days she is a mother-to-be, and draped in another set of threadbare attributions. Once she gets over being sick, the press will find that she is radiant," said Mantel.

"They will find that this young woman's life until now was nothing, her only point and purpose being to give birth."

Mantel also said Paul Emsley's official portrait of Middleton showed a woman with "dead" eyes.

- © Fairfax NZ News