Kate is currently touring the addiction charity's Hope House treatment centre in Clapham, south London.
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.
"I can only speak (of) what I know. 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."