Billie Piper has revealed that playing a high-class callgirl in new TV series Secret Diary of a Call Girl was an educational experience in more ways than one.

To research her role for the ITV drama - based on the blog-turned-blog by the pseudonymed Belle Du Jour, Billie met with sex workers to talk about their jobs: “I met high-class hookers who were very candid.”

“I wanted to know if they get anything out of the sex, if they ever fell in love with the guys. Surprisingly, some did.”

“It’s funny because we sat down with quite a few girls and you have to be very open. You get into it and then you go crazy and say ‘Tell me this, tell me that’.”

“The most shocking thing for me was that I imagined guys wanting to sleep with prostitutes being quite bolshy but it actually isn’t like that.”

“They feel quite vulnerable. These women are man-eaters. It shocked me that it would be like that. These guys get so wound up that perhaps they can’t perform.”

After playing the girl-next-door in Doctor Who, Billie relished “a chance to be shockingly sexy. The sex scenes are choreographed. You talk about where your hand goes and where to put your body - it’s a bit like dancing.”

“[But] I now know how to walk in nice underwear. The whole time people were saying, ‘You’ve got to push your t*ts out, stand straight’. Nice underwear makes you feel quite sly. No-one else knows about it.”

She was allowed to keep many of the sexy outfits she wears in the series and in case that isn’t enough for boyfriend Laurence Fox, she added: “I’ve learned one or two things to take home too…”