Billie Piper tells Andy Welch about her role as a high-class prostitute - and how she got in shape for appearing on-screen in her undies.
When the name Billie Piper comes up in conversation, one of two images tend to spring to mind for most people.
Depending on your age, you might remember her as a fresh-faced popstar, stomping around in the colourful Because We Want To video, although more recently her name has become synonymous with Doctor Who's cockney tomboy Rose Tyler, who she played for two successful series.
Miss Piper, however, has never been associated with high-class prostitution before, but that may all change thanks to the new ITV2 drama, Secret Diary Of A Call Girl, in which she plays call girl Belle de Jour. 'Belle' - her real identity has never been revealed - worked as a high-class escort in London for years, before detailing her exploits in a famous online blog and later in two books, The Intimate Adventures Of A London Call Girl and The Further Adventures Of A London Call Girl.
So far, Belle, whoever she may be, has sparked massive controversy with her memoirs, and the TV series, complete with raunchy scenes and candid dialogue, is likely to stir up a storm all over again.
"It's intimate," says Billie of the eight-part series. " Really intimate! I'm really scared, if I'm honest. Well, just ... I'm quite nervous, you know, because of the nature of the show.
"I hope people think it's been handled well and that at times it makes people laugh, and that people can get over the initial shock factor of the piece."
It may indeed come as a shock to some viewers to see Billie writhing around in her underwear, and of course, in some scenes, doing what prostitutes do - having sex - but the young actress is more than aware of what she's letting herself in for.
"It's quite scary thinking people are going to see you in that way for maybe the first time, and that people may treat you slightly differently," Billie admits.
"But I considered this job more than I considered anything before. It's such a different world to what I know.
"Obviously it's quite full on and it's relentless. It's not just one sex scene here and there, it's ... endless!" she laughs.
"But if I'd jumped at the chance of playing her, people would have raised their eyebrows and thought 'You little slag!"'
Of course, many of us would happily admit that acting out such scenes in front of a room full of camera crew would make us blush, but Billie maintains she didn't get embarrassed by the more steamy scenes because of how mechanical they became during filming.
"You talk endlessly about it, and you choreograph it like a contemporary dance. You're also briefed heavily so you know what you're about to get yourself into," she explains.
"You have to do a lot of motivational speaking to yourself every single day. I couldn't be shy about it if I was playing a hooker.
"You can't get precious about what you show, because you're playing someone who has sex for a living. I just couldn't really get prudish about it."
As viewers will soon find out, Billie spends a lot of time in her skimpies, but she looks good, make no mistake. So is her super-toned body the result of hours and hours in the gym?
"No, not the gym," she says emphatically. "I don't like the gym at all, makes me want to kill myself. But I have been running outside quite a bit, and I'd just finished a play.
"If anyone wants to lose weight, that's the way. The fear alone will keep you slim, so thank God the role came on the back of that and not after Christmas!"
Despite winning a Guardian newspaper award for Blog of the Year and publishing two books, there is still some doubt by sceptics as to whether 'Belle' was a real person.
Real-life working girls say her accounts are too good to be true, and infamous madame Cynthia Payne totally dismisses the London Call Girl series as the work of a male author merely having a go at writing posh porn.
Billie, however, insists that she met the real Belle, who helped her to prepare for the role.
"I definitely did meet Belle, and she's sweet and she's interesting. She's very clever as well," Billie says.
"She's cool, incredibly well read, witty and her writing style is not out of character. When you meet her, it's definitely her voice. It all feels very real to me.
"I don't know what it's like to be a hooker. It's such a taboo subject, you just hear all these horror stories, so it's quite hard to get your head around the fact someone has done it out of choice and they actually enjoy it, love sex and love getting paid loads of cash for it.
"That's quite a hard concept to get your head around initially," she continues, "because you think, 'Well, obviously there must be something quite tragic in your life', you know? So it was really helpful, meeting her, seeing her. She's so well turned out, graceful, elegant."
As well as being impressed by the former call girl - who has apparently now given up - Billie had a few questions of her own for Belle.
"I wanted to know when she was with a bloke, what their faces were like, " she says.
"I wanted to know if they were bolshy and turned into egomaniacs or power-freaks," Billie clarifies.
"Belle told me that it was quite the opposite. Men get really scared and vulnerable and nervous, worrying about if they are going to be exposed to the point where they can't perform. I didn't think it would be like that, so it was quite fascinating really."
Billie then goes on to say how the role challenged her preconceptions of prostitutes, and thinks that it may do the same for viewers, but is unwilling to get into any debate surrounding the issue, and whether or steps should be taken to legalise the oldest of professions.
"It's a tricky subject, you know. I'm sure families will be up in arms, " she sighs. "And I'm sure some will say you're just advocating prostitution. You're making selling your body and soul desirable, like it's some kind of reality TV show", so I'm quite aware some people will find it a bit offensive.
"But I'm just telling this girl's story and, in this instance, it wasn't like sex trafficking," she continues. "This is a woman who said 'I chose to do it and I f****** love it, and if that makes me wrong then I'm wrong.'
"Ultimately, some people don't live the way we live. Some people don't conform in the way that I do, and some people have their own very different set of rules and morals.
"It doesn't make them a*******s; it just means that they're different," she smiles.
Secret Diary Of A Call Girl, ITV2, September 27