The TV host, 60, said politicians did not expect to get a grilling when they agreed to talk to her.
Asked by BBC Radio 2 DJ Ken Bruce whether being underestimated had benefited her career, Kelly replied: "It has helped massively. I would never put them right and I still don't.
"They think they're going to come in for this lovely wee ... interview and yes, it's a chat, a conversation more than anything else.
"But yeah, especially politicians, (they) can really underestimate you until they get asked the question that makes them go all funny."
She told the radio show: "It's good, I don't knock it."
Kelly hit the headlines last year when a judge in a tax tribunal case said that the Scottish star "presents a persona of herself".
The Lorraine show host won the £1.2 million battle with HMRC, with the tax tribunal judge stating that she was not an ITV employee and she performed "the role of a friendly, chatty and fun personality".