Whips, sexy undies and stilettos - Billie Piper talks about her brave new role in Secret Diary of a Call Girl

You get to wear all sorts if risque outfits in The Secret Diary. What are your favourite clothes?
As most people probably know I’m happiest in trampy clothes, just being comfortable. I’m a real tomboy and at first putting on those glam clothes felt alien to me. I didn’t feel 100 percent comfortable but very quickly I grew to love my costumes and often I wouldn’t take my heels off even when I was on the way to the catering van for some sausages.

Do you find costumes help you when playing certain roles?
Costumes are so important when acting, I never used to understand it but the minute I put on one of those sharp tailored suits and a pair of stilettos I instantly felt different. Personally I dress for my mood every single day.  If I want to feel strong and empowered I’ll wear something that suits that mood, when I feel slightly romantic and chilled, or a bit dipsy I’d wear something floaty and have bare feet. These things do have an effect on the way you behave and the way you see yourself.

Is underwear important?
What I’ve discovered about great underwear is that you can wear it secretly. No one else needs to know you’re wearing something fabulous under your clothes. You just do it for yourself and it makes you feel great – empowered and body confident.

Why did you take on the role of Belle?
“It was Belle, the person portrayed in the book that drew me to the project. I found her absolutely fascinating and some of her ideas quite romantic plus I liked her style of writing.  I thought she was funny, witty, sharp and intelligent and I liked the idea of playing her.

The subject of prostitution is a sensitive one isn't it?
This is such a taboo subject, no one really ever speaks about it except the horror stories about the nature of the work.  It was certainly a very different story to every other one I’d heard about prostitution.

You met the real Belle. How was that?
Meeting Belle was really helpful. There is so much speculation surrounding the book; is it true? Does she really exist? Have these things really happened? Is she romanticising something quite controversial? Meeting her took the fear out of the part I was venturing into.

Did she tell you why she became a call girl?
She explained exactly how she got into it for reasons I could completely understand. I couldn’t do it myself per se but I can understand how she found herself in that situation and why she continued to do it.  It was good to see her, watch her behaviour and mannerisms. We spoke about the music she likes, she’s so incredibly well read and cultured, a fascinating woman. It was good to sit down with her one- on-one and ignore all the shit that surrounds the subject mater and have a very honest and frank conversation.

Did she tell you how she got into this sort of life?
She likes sex this woman, she loves it and she found herself living in London with about £20 to get through the month. One night she was at a dinner party that turned into an orgy, she left and discovered she had cash in her hand. The job she does isn’t for everyone but you have to try and understand why somebody does this and what effect it has on their life. I’m sure there are many down sides but Belle enjoyed what she did and felt very much in control of it.

Many women are forced into prostitution but for Belle she made that choice, didn't she?
That is a major point, being a prostitute was her choice, she wasn’t forced into it. It’s not about sex trafficking and it’s not drug related at all.  Obviously these things go on but I’m just telling this one person’s story. Everyone knows that prostitution can be hideous, abusive and destructive. We’re often told about it in the media but I’m playing the woman who wrote this book, and she has a very different story to tell.

Are there any differences between the TV Belle and the real-life one?
The obvious differences are that our Belle is a touch younger and a lot greener. She’s not been in the game that long, 18 months into it and she’s still learning about the downside of her chosen profession – spending a lot of time alone and finding it hard to form relationships.  Belle is still new to her work but has the same kind of energy and thought process that the original Belle does.

Does the fact that this is a true story make it more compelling?
I think it’s always better watching something that is a real story; it makes it more fascinating.  Sex is interesting, the way people behave in that situation especially when money is being parted with. It’s something we know nothing about unless we’ve taken part in it.

How did you find filming the sex scenes?
Naturally the series contains many sexy bedroom scenes and even when filming on a closed set these can be exhausting for the actors taking part. It’s tiring filming sex scenes.  Those days when you maybe have two sex scenes to do, you just want to be over and done with but they are vital to the piece.   We’re telling the story of a hooker, you can't be shy about sex.

Are all sex scenes the same?
There are two different kinds of sex scenes – the comedy sex, which is entertaining and funny and the emotional sex with regular clients like Ashok, who is someone that she cares about and could quite possibly be her boyfriend.   Those are harder.  I just had to get on with it and not be shy.   What I do is channel my thoughts, turn into bit of a robot.  You have to be quite frank and a bit mechanical about it at times – ‘I’m going to put my hand here, can you put yours there. I don’t want to show this bit of my body’ and so on.  You have to be honest about it and sometimes quite crude. But like anything those things become very normal very quickly – well they do to me!

There is an S&M episode. Did you get any advice for these scenes?
We had a genuine dominatrix on set, she was really sweet and cool and fascinating. I just kept thinking whereabouts in London do these things take place and who do they take place with?  What drives a person to do that and what do you get out of it?  Our ‘domme’ was open and candid, really insightful.  I had quite an education.   Like with most of these things it’s all about control and ego, whether letting go of control or acquiring control. It’s quite easy to understand once you work out the premise of the whole thing.

Could you be a dominatrix?
I know I couldn’t do the job, I’d be endlessly concerned about hurting them, what effect it would have on me or would I scar them for life - emotional or literally.  Sometimes it is about handing over complete control to someone else, letting them make every single choice for you and I can understand that theory and it must be quite liberating.

Is there a danger that the series could glamorise prostitution?
If it was just a male crew making the show, I’m sure people would be slightly sceptical about the piece and what it means and women could get slightly feminist about the whole thing.  But these are really strong independent women who know their stuff and have heavily researched this.  It’s a responsibility to take on and tough to handle and these women are very clever and are not exploitative, they are just telling one woman's journey.