Hilary Mantel's remarks about Kate Middleton are so wrong: David Cameron

David Cameron said on Tuesday that Hilary Mantel had been "misguided and completely wrong" to describe the Duchess of Cambridge as a "plastic", "machine-made princess".

The Prime Minister interrupted his trade visit to India to lead a public backlash against the double Booker Prize-winning author, who claimed that the Duchess's "only point and purpose" was to give birth.

Mantel was keeping a low profile, as her agent implied her comments had been misinterpreted.

The Wolf Hall author described the Duchess as "painfully thin" in a speech, and "a shop-window mannequin, with no personality of her own".

In response, Cameron said, "I think she writes great books, but I think what she's said about Kate Middleton is completely misguided and completely wrong.

"What I've seen of Princess Kate [sic] at public events, at the Olympics and elsewhere, is this 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."

Ed Miliband, the Labour leader, also weighed in, saying, "These are pretty offensive remarks, I don't agree with them. Kate Middleton is doing a brilliant job in a difficult role. She's a huge asset to the country. She deserves our support in the roles that she's playing."

As luck would have it, the Duchess spent yesterday drawing attention to the work of a charity for drug and alcohol addicts, in a public engagement that could not have done more to undermine Mantel's comments.

The Duchess, who showed off her pregnancy bump through her flimsy Max Mara dress for the first time in public, admitted to being nervous about giving birth. Lisa, 34, a recovering alcoholic at the Action on Addiction recovery centre and mother of three, said: "I asked her [the Duchess] if she was nervous about having a child and she said it would be unnatural if she wasn't."

The Duchess was not asked about Mantel's remarks as she visited the centre in Clapham, south London, of which she is patron; but the charity's chief executive, Nick Barton, described their royal visitor as "engaging, natural and genuinely interested in the subject".

When The Daily Telegraph asked Mantel's agent, Bill Hamilton, if the author wanted to respond to Cameron's comments, he said only, "Read the original article." In the London Review of Books lecture, delivered earlier this month, Mantel said: "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.

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

Prof Mary Beard, the historian, leapt to the author's defence, saying, "I would just urge people to read or listen to the whole lecture?…? which didn't come across to me as a venomous attack on the Duchess, but as a bit of coolly dispassionate analysis on the 'female royal body'.

"It was as much about us, and our investment in the 'body of the queen', as it was about Kate Middleton. I would say that the attacks on Hilary Mantel seem to be based on a misunderstanding of what the lecture was really about."

Kate Williams, the historian and royal biographer, agreed that the row had been taken out of context and that Mantel was commenting on the portrayal of the Duchess and not her actual character.