It's hard to imagine Wiltshire actress Billie Piper, glamorous star of stage and screen, donning a pair of marigolds and giving the kitchen a good scrub.

But when she's not busy filming or looking after little Winston, her one-year-old son with actor hubby Laurence Fox, Billie loves to indulge in a bit of housework.

"It's not cleaning for me, it's like something else... something wonderful and magical!" said Billie, who is back on TV on Thursday night in the third series of ITV2's Secret Diary Of A Call Girl.

For a girl whose showbiz career took off with a record deal at the age of just 15, Billie is surprisingly unaffected.

At 27, she seems rooted and mature. These days, there are none of the paparazzi pictures that dogged her marriage to Chris Evans - the pair got hitched in Vegas after just six months back in 2001. Instead, she and Laurence avoid the limelight all together.

"I suppose you have to go to the right places and we just don't want to," she says with a laugh, tucking her legging-clad legs beneath her on the sofa we're sharing.

"I've done all that - we just hang out at home with our friends. If I wanted to go and see a film, I'd go and see it at the cinema instead of going to the premiere.

"We just don't live that life at all. It's not because we're trying to make a statement and we think people who do live like that are wrong, it makes us very nervous. We're quite nervous people."

Nervous? This is Billie Piper, the youngest singer to debut at No 1 back in 1998 (with Because We Want To), who's since wowed TV audiences and critics with roles in Doctor Who, and stripped off in Secret Diary Of A Call Girl.

"It's a weird kind of contradiction," she admits, sensing my consternation. "But if you thought about all the people [watching you on TV], when you were filming something, you'd probably f*** it up."

Swindon-born Billie was back on our screens at New Year, briefly resuming her role as the Timelord's sidekick in David Tenant's final episode of Doctor Who.

"It's always quite nerve-wracking picking up a character you haven't played for a while," she says. "I was filming Belle de Jour [in Secret Diary...] at the same time, so I went from that during the day to Doctor Who at night. It was tricky, but it's always nice to be in that company."

While that's the last we'll see of Rose, sassy prostitute Belle is back for a third series on ITV2.

In November, the real life Belle, whose blog was immortalised in a book and the TV show, came out as 34-year-old cancer research scientist Dr Brooke Magnanti.

After enduring two years of criticism over her choice of role, Billie's clearly relieved by the revelation.

"It's nice to share the load, to finally have someone come out and speak up and say her piece and defend what she's done."

Billie had met Belle as part of her initial preparation, but says she never had a problem keeping her identity secret.

"I just didn't tell anyone!" she laughs. "I didn't really meet her, I knew nothing about her apart from what she'd said in her blog and her book. I didn't get an insight into who she really was, I didn't even know her name was Brooke."

The pair have met since for a TV show called Billie And The Real Belle Bare All, which kicked off the new season of Secret Diary.

In this series, we see Belle dealing with the highs and lows that come with the publication of her first book.

"She's taken on a whole new role, she's a published author, she's a prostitute, she's a girlfriend, there's all these things going on in her life and it's about how she juggles them and how they kind of cross over and how many grey areas there are."

She's also under pressure to find some juicy new material for her next book.

"The editor encourages her to make it more compelling, so her encounters with men just get way out of control. Not in a nasty way or dangerous way, just more fantastical with role play, sex with food, it's just quite out-there.

"The flip-side of that is her personal life. She falls in love again and she's forced to question her profession - and her friend Bambi gets together with one of her clients and that's obviously a big no-no for Belle."

Last series, Billie was pregnant with Winston and had to use a body double for her naked scenes. This time she was able to do more, but admits there's still "a line drawn in the sand".

"There are some things that you just don't want to do!"

She recently admitted that she has even questioned her choice of role now she's a mum - and she still gets stick for 'glamorising' prostitution.

"You're talking about prostitution and not exposing it in a way it's normally exposed, which is brutal, beating, murder and rape, all those things we're used to seeing.

"It's so radically different that I think it scares people because they just don't understand how any woman would be seemingly OK with it."

Does Billie understand Belle and other women like her?

"I'm in two minds about whether I think it's OK, whether it's wrong, whether it should be legal, I'm really torn.

"I've met all these girls who are OK with what they do and I've looked at them really hard for the tell-tale signs of someone who's been tortured, or some tragic tale, or some story of neglect or abuse even, or drugs - and they're just normal girls, it's bizarre.

"You expect to see something else and you don't and you have to believe them because that's what they're telling you."

Like many women in modern times, Billie's confused by how women should behave.

"Sometimes I feel like a walking example of modern woman with feminist ideas and other times I'm a real traditionalist. It's really hard for guys because we want them to back off and let us do our thing, but at the same time we want to feel small in their company."

She and Laurence split the chores at home - she does the cleaning and cooking and he does "loads of jobs I just can't bear to do".

With a grin, she adds: "We fight though, don't get me wrong, it's not some perfect blissful arrangement!"

Winston's arrival has changed the way she works and the family's routines - her mum does some of the childcare and they've had a nanny - but although Billie's no longer the wildchild she once was, she hasn't changed inside.

"I was expecting to feel something quite different and I just don't feel like I am. It's probably because I've gone back to work, so I'm endlessly reminded of who I was before.

"I do feel like I have to be more responsible, I feel like I can't be as reckless and spontaneous as I once was, but that's the only difference, I don't feel like I've got some new profound sense of what the world's all about.

"I definitely feel more complete, like I have a purpose in life - you're never going to feel bad about taking care of your child, but you might feel bad about always being at work. But I don't have some new profound philosophy."