The Secret Diary of a Call Girl star talks sex scenes, motherhood and the new Doctor Who.

What’s in store in the new series of Secret Diary..?
“It’s quite radical. Belle’s now an author, and her editor Duncan, played by James D’Arcy, wants her to find more outrageous clients to fuel her writing. I couldn’t do sex scenes for the second series because I was pregnant, so I suppose I’m paying for it this time around.”

Is there any romance on the horizon?
“Her relationship with Duncan is weird and complex. He doesn’t judge her, he encourages her, and she finds that confusing. Apart from her friend Ben, he’s the only guy Belle can confide in.”

How did you feel about the real Belle, Brooke Magnanti, losing her anonymity last year?
“It must have been liberating to unburden herself of that secret, but also frightening because now people will recognise her as this woman who had sex with loads of men. It’s nice for me to share the load with someone though, because I feel I have become the face for prostitution.”

Do people treat you differently now?
“Men don’t come near me, but maybe that’s because I’m married with a child. I think some people believe I actually do it for a living, or feel that it’s irresponsible of me to play Belle, having come from family entertainment. ‘You’ve disappointed us, Billie Piper – you were Rose in Doctor Who!’ But I can’t play Rose forever.”

Does anything about playing Belle faze you?
“The more intimate, loving stuff is tricky because you have to imagine the emotions. The sexy stuff is just funny, but there are days when I leave the set feeling grubby, and I suppose I might regret that one day. I knew what I was getting into when I took the job on.”

What do you think of Matt Smith being the new Doctor?
“I’ve worked with him before and he is amazing and a great choice. We’ve spoken briefly, but I don’t know how to prepare someone for the impact the show has. Your entire life changes and, while it’s great, it’s also hard, as you’re followed everywhere.”

Secret Diary has done well in America. Would you like to work there?
“I might go out later this year to meet casting directors, but working there takes so much commitment and I worry about my family. I can’t just say, ‘I’m off to America for a month – deal with it’.”

What’s next for you?
“I have just finished a Kay Mellor drama called A Passionate Woman, which will be shown in the cinema and then on the BBC. I play a married mum who falls in love with her Polish neighbour in the 1950s. Sue Johnston plays my character 30 years on.”

Secret Diary of a Call Girl returns to ITV2 on Thursday January 28 at 10pm.