The Duchess of Cambridge has arrived at an addiction treatment centre for a royal visit as the furore surrounding Hilary Mantel's scathing criticism of her continued.

Kate travelled to Hope House treatment centre, in Clapham, south London, in her role as patron of Action on Addiction, to meet women who are rebuilding their lives.

But the visit was in danger of being overshadowed by Mantel's comments, made during a lecture at the British Museum when she criticised the Duchess as appearing to have been "gloss-varnished" with a perfect plastic smile in contrast to Princess Diana, whom she described as awkward and emotionally incontinent.

She went on to suggest that the "painfully thin" Kate was selected for her role of princess because she posed no risk of showing any character.

Nick Barton, chief executive of Action on Addiction, defended his royal patron, describing her as an "intelligent" woman genuinely interested in the work of his organisation.

Asked for his reaction to Mantel's criticisms, Mr Barton said: "I don't think it's for me to comment on that kind of stuff - I speak of what I know, somebody who wants to help, is helpful and genuinely interested and is intelligent."

He added: "I've met her several times and I found her to be engaging, I found her very natural, I found her actually genuinely interested in the subject. You can tell a lot from people's questions and she asks really good questions. They're not routine stuff, they're questions of someone who wants to learn. I find her very easy to deal with."

A large media presence had gathered outside the treatment centre, with satellite vans for broadcasters lining the road, and photographers standing three deep on the pavements.

Mr Barton greeted Kate when she arrived and, looking tanned after her Caribbean holiday, she got a large cheer from well-wishers standing across the street.

The Duchess, who is more than four months pregnant and wore a MaxMara dress, clasped her tiny baby bump for a moment before heading inside Hope House.