CHART-TOPPER at 15, anorexic at 16, washed-up star at 17, teen bride at 18, Hollywood stay-at-home wife at 19, drama student at 20, single woman at 21, born-again celebrity at 22, author at 23, fully-fledged TV star at 24.

Yes 24. It's hard to believe that Billie Piper is still only 24.

Having written her memoirs, in which she documents how she walked away from her parents, the music industry, marriage to media darling Chris Evans, and her role as Rose Tyler in Wales-made Doctor Who, she is off again, this time into the world of theatre and Jane Austen on the box.

In the latter's Mansfield Park she plays Fanny Price, a young woman who is old and wise beyond her years - just like the star herself, perhaps.

She was, she says now, somebody who found childhood dull.

"I always wanted to be a grown-up. I was so bored with being a kid, and being at home, and having to go to school. I just wanted to work, and I found it quite suffocating. When I was younger I was so ambitious. I'm still ambitious now, but I don't have the hunger I did, say, when I was 10 years old. I was certainly more fearless then, and more selfish, and just wanted to do exceptionally well."

Which she has done, of course - but it has come at a cost.

When she sits down for our chat, she looks like a frightened rabbit caught in the headlights. And it's hardly surprising that she's in a bit of a whirl.

Any meeting with the Press right now must seem like an extra burden of contractual obligation, in what could be seen as the most tumultuous and far-reaching time of her career.

Billie has just made her West End stage debut - to rave reviews, incidentally. But most of the gossip columns seem happier to speculate about the relationship with her co-star Laurence Fox than to talk about "the work".

Have they set up home together? Are they getting married? We won't get those answers here.

Added to all this has come a debilitating bout of gastric flu which kept her from some preview performances at the Garrick Theatre - though she did make the crucial opening night, where her triumphant turn in Treats, Christopher Hampton's once-forgotten, three-hander black comedy of sexual manners, garnered generous phrases like "powerful and impressive" from some of London's most hard-to-please critics.

Try and ask her if Fox (son of veteran actor James) has been a welcome support during this time, and she cleverly diffuses the situation with a much more general response, steering away from her private life.

"Laurence and Kris have both been very supportive," she smiles - also referring to her other co-star in the play, Kris Marshall of My Family fame.

"They've done it (theatre) before, so that's really helpful."

She does, though, admit to finding the whole theatre experience "amazingly stressful".

"This play has been occupying my thoughts morning, noon and night.

"It's the first thing I think about when I wake up. It's good, but it's hard. It's a very different discipline and technique. It's highly stressed and you need a lot of concentration.

"For TV you need to have a few minutes of intense concentration and then you can go and have a cigarette and a doughnut and it's quite chilled. But I'm likely to learn a lot more as an actress on stage than if I stayed doing TV for the rest of my life. It's quite good to mix it up."

These, then, are heady, busy, crowd-pleasing times for both Billie and her latest boyfriend, and neither is content with just the polite applause and luvvie laurels of the West End cognoscenti.

Fox has just appeared as Kevin Whateley's posher sidekick detective in three episodes of Lewis, ITV1's risky yet smash-hit Inspector Morse spin-off, pulling in around eight million viewers a time.

And not to be outdone, Billie is about to court the same viewer demographic by taking the lead role in the opening drama of the same channel's lavish Jane Austen season, Mansfield Park.

This is not her first venture into period TV drama - at Christmas she starred in BBC1's ratings winner The Ruby in the Smoke, an adaptation of Philip Pulman's Victorian potboiler mystery, and she's already filmed a follow-up, as the same character Sally Lockhart, with The Shadow in the North, due for transmission later this year.

Although she may be an award-winning actress with a couple of hit series like Doctor Who under her belt, Billie still worries about work.

"I freak out about everything," she admits. "I'm one of those people who pretends they're not neurotic but secretly I'm a complete neurotic. I'm one of those very annoying people. I get quite panicked about everything, but it's only because I care so much and want whatever I'm in to do well. It doesn't come from a bad, selfish place."

It's likely then that Billie felt particularly nervous about leaving Doctor Who and her character Rose Tyler behind last year. But it seems to have paid off.

Just a few years ago, playing the lead in a flagship ITV1 drama may have seemed a distant dream to Billie, whose fledgling pop career looked to be all but over at just 17, when her single Walk Of Life flopped in the charts.

However, following her high- profile marriage to TV presenter Chris Evans a year later, and their subsequent split, she reinvented herself as an actress.

"It's surpassed my expectations really," she says. "I've had a really good three years. It's been an exciting time to be alive. And I hope it may continue in the same way."

But success comes at a price. Her love life has come under intense scrutiny and she's long been a media target.

"I don't read it," Billie says firmly.

"I used to read everything written about me and it sent me mad. I just find, if you don't read it, you just don't care. You can let that kind of thing dictate everything you do, and then it's not really about the work, it becomes about what people think about you. So I just try not to listen or read, and just get on with my life."

And what a life it has been.

In her autobiography, Growing Pains, she reveals her burning ambition from childhood and her insatiable workaholic mentality, from first attending the famous Sylvia Young theatre school when she was 12, to becoming a pop star at 15, when she effectively lost control of her life.

Her first single, Because We Want To, went straight to No.1, followed by Girlfriend, which also topped the charts.

She is still the youngest female to have a UK number one.

Her hugely hectic work schedule - 18-hour days, recording, making videos and touring - meant her life became far removed from the normality of her family and friends in Swindon.

It was then the feelings of self-doubt engulfed her. Was she thin enough, could she sing well enough, could she pull off live performances?

"The anorexia turned into something which was about me losing control of every aspect of my life and knowing that the one thing people couldn't force me to do was eat. It was me being rebellious and finally having control over something."

She lived on a diet of cigarettes, coffee and Diet Coke, then moved on to laxatives. At one point she became so ill she stopped menstruating.

"I went down to about seven stones. At the time I thought I looked fabulous but I look back and realise I looked like a freak."

The pressure Billie inflicted upon herself to remain at the top all but destroyed her. Sitting in empty hotel rooms night after night, she'd reflect on her success and wonder why she didn't actually feel anything.

She pushed her worried parents to one side and for much of the time they had no idea where she was or what she was doing.

"I yearned for stability when it suited me. I was incredibly selfish. I would row with my parents and not talk to them for weeks and then suddenly I'd be in a car on my way home having been out all night and turn up on their doorstep saying, 'Take care of me, please'."

Matters reached crisis point in 1999 when, in a hotel room in Chicago, she made a feeble suicide attempt with a handful of Melatonin, which she thought were sleeping tablets, before calling her parents in desperation.

"I don't know how much of it was teenage angst," she says now. "It was a half-hearted attempt, a cry for help."

Billie had begun her recovery when she met Chris Evans as a guest on his Channel 4 TFI Friday show. She was 18 and he was 34.

Shortly afterwards she appeared on his radio show.

"He was my knight in shining armour," she laughs. He was so taken with her that three days later he delivered a brand new £100,000 Ferrari covered in roses to her house.

"He has this zest for life that very few people have," she beams. "He's the forever optimist. He's had some terrible times and some fantastic times. Wonderful things have happened to him, but only because he's gone out there and made them happen."

He wasn't aware of the anorexia initially and when they first started seeing each other, it would often be for a meal.

"Whenever we were out together I would eat. It changed just like that," she says, snapping her fingers. "He made me feel so sexy and happy about myself. That's his gift."

They married in Las Vegas in 2001 and enjoyed two years off when her pop career waned and he fell out with Virgin.

During that time, they were pictured in different places all over the world, often hammered and dishevelled.

She laughs at the suggestion that they were permanently plastered during those 'gap years', as she calls them.

"There were elements of that, for sure," she smiles. "But we were also learning about the places. We weren't going to Athens to sit in a bar and get plastered, we were going there to see things that were there."

That phase came to a natural end, she says, when both of them decided they wanted to return to work. They came back to live in their big house in Surrey. She cooked, grew vegetables and went to bed at 9pm.

But she also re-launched her acting career, gaining the part of Rose Tyler in BBC Wales' Doctor Who, which took her away a lot.

"It's really hard to say what went wrong. He didn't have an affair, I didn't have an affair, he didn't abuse me, it's all a bit vague.

"We had been inseparable and suddenly we never saw each other. That was just too hard for us and our relationship. We fixed each other and then we had to go and do some stuff of our own again.

"Chris and I are best mates. We speak all the time. I call him like I would a girlfriend."

Billie says their continuing closeness didn't make it difficult for her to have another relationship, although they are still not officially divorced.

These days, with a failed yet happy marriage behind her, it's the work which takes up the lion's share of her time. She's now in huge demand and is clearly excited about her projects and obviously in awe at being asked to be a part of the "big deal" that is an Austen production.

"I was thrilled to be asked," she smiles.

"I remember auditioning for period pieces at school and people always said, 'She doesn't have a period face,' and getting really frustrated. I'd say, 'That's not the point! I can work it out!'

"It's such a privilege to play a part in an Austen drama. My gran couldn't be happier. She almost cried when I told her, she thought it was brilliant news. It was easy to say yes to. It's a great part, and a privilege to be part of an Austen. And Fanny is a lovely wholesome girl and it's quite nice playing parts like that."

The drama sees Fanny Price taken from the poverty of her childhood home to live with rich cousins at Mansfield Park, where she forms a close attachment with one of her cousins Edmund (Blake Ritson). However, his head is turned by the visit of Mary Crawford from London and it looks like Fanny may have lost out on love. But, of course, in typical Austen fashion, it turns out happily in the end.

"Austen books are special and lovely," Billie says. "They're obviously a great read, but what I love about Austen is that you root for good people to get together, more than you do with dramas and films."

But Billie found it frustrating to play a woman in Austen's era, where ladies were repressed and under intense pressure to secure a good marriage.

"It surprises me that Fanny didn't have a stomach ulcer because she can't voice what she's feeling.

"She confides in Edmund but that's the only person who asks her opinion and is interested in what she's going through. So all of it is going on inside and it's quite oppressive. And she's so curious as well, which is even more frustrating.

"I'm nothing like her, but I wish I was because Fanny is a much nicer human being than I am," she continues. "She's so incredibly compassionate and loving and wants the best for people. Her heart is firmly in the right place. You come away wanting to be a better person when you've played Fanny Price."

But playing her wasn't altogether a comfortable experience.

"The novelty of wearing a corset wears off after about five hours," Billie smiles. "When you realise you have to drink isotonic drinks and not eat too much food. It's kind of like, 'I want to take this off now'.

"But wearing it is special and it really helps you to get into character. During rehearsals, I was playing Fanny in my jeans and Converse trainers and it was hard to convince myself, let alone the audience. So it's nice to get the costume on and get on set."

Fanny was Austen's personal favourite out of all her heroines, but also one of the most troubled, unsure and introspective. Some might suggest that Piper is too pretty and extrovert a type to play Fanny, generally regarded as a plain, demure type.

But ITV1 clearly needed a big, populist star to launch its impressive new "range" of Eng. Lit dramas, which once would surely have been the exclusive domain of the BBC.

Billie, however, now a seasoned performer, had no qualms about taking on the role, other than standard nerves.

"Fanny is such a lovely part," she says. "She's a wholesome woman. It makes you feel healthy, playing this part.

"What was really important for me was that I was able to bring my own ideas to the part, and that's what was great about our director, Iain B Macdonald.

"He wanted it to feel really fresh and young and loose.

"You know how period drama can sometimes feel pretty stuffy and quite boring?

"Iain has done the entire piece on hand-held camera, so it feels like you're spying on this family, which is what I love about it."

Romance comes for Fanny Price, eventually, with her cousin Edmund.

"Oh he's lovely, so funny, and he has more energy than almost anyone I've ever known," says Piper.

"In fact his energy levels are on a par with David Tennant (who plays Doctor Who) and he eats like a horse, which is mad, seeing the size of him.

"On set, he always had his pockets full of food."

The blossoming relationship between the two was another reason she was drawn to the part.

"I'm a hopeless romantic," she adds.

"It's a lovely idea that there's just one person for you. If that can happen in your life, that's quite special. I think that's why we quite like these stories and these films because they are incredibly romantic and magical."

The role of Fanny required a small amount of horse-riding, a lot of dancing, and plenty of Regency-style etiquette.

"I didn't have any side-saddle riding," says Billie. "Luckily there wasn't a great deal to do.

"There's a wide shot of Fanny galloping on horseback across a field, but that's not me, unfortunately.

"I was very excited, though, because the girl who's my stunt double can ride faster than Blake's stunt double so it looks like Fanny is a much better rider than Edmund!"

There was likewise little time to practise the very specific style of late 18th Century dancing.

"The dancing makes me hysterical because it goes on for so long and it's a big group dance - if one of you puts a foot out of place, it's like the domino effect, everyone falls about and loses it," says Billie, breaking into genuinely hysterical laughter.

"It's really funny watching the boys dance because, in the nicest way possible, they don't all have natural rhythm. That was a fun day."

The shy, modest Fanny Price is about as far removed from streetwise time-traveller Rose Tyler as you can get, and it's a deliberate avenue of direction for the actress.

"I did mean to do something completely different and quite far removed from Doctor Who, and I want to continue doing that if I get the chance," she explains.

"I think it's good to keep challenging your ideas. Otherwise I think you can get complacent and quite stale, I don't ever want to experience that, because I love acting so much.

"I just felt it was time for a change from Doctor Who. I think you know when it's time to move on - well, I certainly do with most things.

"Two years in Cardiff is quite a long time, and I wanted to get back to London and have a crack at other things."

In Growing Pains, she speaks fondly of her time making Doctor Who in the city.

She said she turned her rented flat, in the former St David's Hospital on Cowbridge Road East, into a "show home".

"I'd wash and iron, dust and hoover, to my heart's content, then pop over to the local Spar to buy half a roast chicken.

"It wasn't as sad as it sounds - I liked the routine and the order."

Billie said she enjoyed filming the second series, with David Tennant, even more, adding, "I wasn't the new girl any more. I knew my way around Cardiff, I knew the crew and I had the pleasure of getting to know David."

Unlike most actresses, Billie isn't sure if she wants to head for the bright lights and notoriety of Hollywood.

"It would be great if the right job came along and I was fortunate enough to be involved," she muses.

"But I really would have to consider it a lot, because I like going to America and staying anonymous and I wonder how much I would want to be in a really big film.

"I don't know if I would want to risk it, as there isn't any going back. I go to New York all the time and I can just be silent and do things like everybody else.

"And I love working here. Telly is really exciting at the moment for me.

"I love being with my mates and family, so I just don't know how much I'd want to leave."

But in the meantime, Billie has more pressing concerns. Like whether to tune in to the latest series of Dr Who, complete with new assistant Martha Jones, played by Freema Agyeman.

"I might find it quite hard," she says. "But I'm going to try. I want to see it, as I'm really intrigued.

"I did watch the Christmas special of Doctor Who. I thought I was going to be a real cat about it, but it was quite easy to sit down and watch it.

"I was pleasantly surprised, and I thought perhaps I will be OK watching the next series.

"I did cry a lot - but then, I was really drunk when I watched it. With my mum, who was also hammered!"