Britain's Catherine, Duchess of Cambridge pays an official visit to the Hope House residential treatment centre, run by Action on Addiction for recovering addicts.

London - The Duchess of Cambridge on Tuesday admitted she was nervous about giving birth, as the British Prime Minister stepped in to defend her against novelist Hilary Mantel.

Kate, who is more than four months pregnant, revealed her baby bump for the first time at a public engagement when she visited a treatment centre run by the charity Action on Addiction.

She spoke of her worries about the birth as she chatted to a group of women recovering from drink and drug addictions at Hope House in Clapham, South-West London.

The 31-year-old duchess seemed proud of her gently swelling stomach, holding it protectively.

Kate, who is patron of the charity, was asked about her pregnancy by recovering alcoholic, Lisa, as she sat at a table with women taking part in an art therapy class. The 34-year-old mother of three said: “I asked her if she was nervous about having a child and she said it would be unnatural if she wasn’t. It’s just human, isn’t it?”

Natalie, 28, a former drug addict and alcoholic, told the duchess about her own pregnancy.

“I told her I’m expecting a baby at about the same time as her [in July]. She was saying she had been unwell but she was feeling better now.”

It was Kate’s first official engagement since before Christmas, when she spent time in hospital with a severe form of morning sickness.

Earlier, double Booker prize-winner Mantel said in a lecture at the British Museum that the the future Queen was a “machine-made” princess, “designed by a committee”.

The author of Wolf Hall and Bring Up The Bodies also said she was a personality-free “shop window mannequin” with a “plastic smile”.

Unlike Prince William’s mother, Diana, who, she said, had an endearing “human awkwardness” and “emotional incontinence”, Kate was a “jointed doll on which certain rags are hung” and a woman “whose only point and purpose” was to give birth.

On Tuesday David Cameron broke off from leading a crucial trade delegation to India to wade into the issue.

Cameron, who mistakenly referred to the duchess as ‘Princess Kate’ in several interviews from New Delhi, said of Mantel: “I think she writes great books, but I think what she’s said about Kate Middleton is completely misguided and completely wrong.”

He told the BBC: “What I’ve seen of Princess Kate 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.”

Back in Britain, Labour leader Ed Miliband said: “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.”

Nick Barton, head of Action on Addiction, also leapt to Kate’s defence, praising her as an “intelligent woman” who was “engaging, natural and genuinely interested in the subject”.

He added: “You can tell a lot about someone from the questions they ask and she asks really good questions, the questions of someone who wants to learn.”

On Tuesday night a spokesman for Mantel said she would not be commenting on the row but urged the public to read her full speech because “it puts everything in context”. - Daily Mail