For a while it seemed Billie Piper was destined to be written off as the junior partner in a car-crash marriage fuelled by trolleyloads of lager. But there is much more to the talented Mrs Chris Evans than her famous husband. Here, she talks to Rachel Cooke about getting her own way, starring with Orlando Bloom and why she likes a man with a big belly.

Billie Piper arrives at the oddly deserted north London restaurant where she and I are to have lunch without coat or bag, in the manner of a visiting foreign dignitary. In jeans and trainers, her straw hair pulled into a scrappy cheerleader ponytail, she looks exactly what she is: an ordinary 21-year-old who, thanks to a combination of multi-millionaire husband and blossoming acting career, is having the time of her life. Once she opens her mouth, however, you realise that the person trapped inside her peachy body is actually a middle-aged woman.

Believe me when I tell you that there is nothing in the world more guaranteed to make one feel gauche - or uncharacteristically young - than interviewing a former child star. It is not just Piper's immense self-possession I find unnerving; nor the fact that her vowels, as befits a one-time prize pupil of the Sylvia Young Theatre School, are as round and polished as brandy balloons. What really unsettles me, given her tender years, is her dedication to - and rigid belief in - Dr Atkins. Abandon hope all carbs who enter here.

A waitress heaves into view, basket of rolls in hand. Piper smiles, briskly, and shakes her head. 'Bread!' she whispers conspiratorially, after our server has scuttled off. 'The enemy!' Alas, I can't agree. The truth is that I have only refused myself because I had two hot cross buns for breakfast.

'Oh, REALLY,' says my date, eyebrows raised, a tart ring to her voice. 'I see. Well, that's fine. Enjoy! Actually, I was brought up on bread and butter. Every meal, I would have two rounds. So suddenly, not having it as part of my diet is a bit like losing a friend. I find myself hanging round bakeries, inhaling the smell of the pastries. It's quite sad. The trouble is, getting rid of it really does make a difference. I feel much less guilty after I've eaten.' A firm smile. 'Bread makes me feel like such a heifer!'

We look at our menus. Billie is going to have only one course: fish, served with a salsa of tomato and cucumber. No, she would definitely not like potatoes with this. She then gets on with telling me about her new film, which is called The Calcium Kid and stars the 'totally beautiful' Orlando Bloom, who plays a loser British boxer. She is his wife, Angel. 'It's a small part, but quite significant,' she says. 'It was perfect for me, because it's my first film and I was nervous about the whole experience.' Yes, of course she had to audition for the role; she didn't mind that a bit.

Thanks to her earlier incarnation as a pop star, people sometimes forget that she trained as an actress, that it was always her plan to act until - dammit - she was distracted by the offer of a recording contract. 'But I was terrified. I always am with things I care about. The adrenaline comes and I turn into this manic girl.'

She is enjoying something of a boom, acting-wise. Last year, she starred in an updated version of Chaucer's The Miller's Tale for the BBC. She played the wannabe singer wife of a seedy-looking Dennis Waterman - a role in which, it is generally agreed, she acquitted herself rather well. In February, more plaudits came her way when she starred in Bella and the Boys, part of the BBC's care season. The story, about a teenager who lives in a children's home, was told in flashback, so she got to play two Bellas: one of them young and shouty and up for sex in the back of a stolen car, the other a subdued adult. And now there is Angel, who is basically a sweet bunny and the film's love interest. What the three roles have in common is that they truly caught Piper's butterfly-like imagination. Having done premier-league fame once already, she is not in the market for boredom. Her three number-one hits have brought her a big, fat measure of artistic freedom, and she intends to make full use of it.

'I don't have to do things for the sake of them. It means I can wait a while, find the right things. I've got the time to go out and find out about life, observe people and dynamic situations that help me in my work. Ultimately, I'm only ever going to do the things that interest me, that I feel I can do something with. If that means people do not see it [the work], that doesn't really bother me. I need to be part of things that make me feel alive. Even if I'm offered a blockbuster, it may not be right at the time, or benefit me.'

Does she fear failure? Apparently not. In many ways, Piper - as we shall see - is spookily other-worldly. At one point, I find myself wondering if it is the case that, like the Queen, she never carries cash.

But when it comes to her career, she is grit-those-teeth, work-that-butt-off ambitious. 'I'm not hard,' she says. 'I won't step on other people. But in the past, I've always managed to get what I want.'

Naturally, Billie Piper knew what she wanted in life from an unusually early age - and that, whether she cares to admit it or not, was fame and fortune. At 12, she left Swindon, where her father worked as a builder, and moved to London. Once there, she boarded with a great aunt and uncle while attending the Sylvia Young Theatre School (she was in the same year as Matt from Busted and Lee from Blue). Three years later, she was spotted in a Smash Hits ad by Hugh Goldsmith of Innocent Records, who was in search of a girl singer to fill the gap in the post-Spice market. At 15, her debut single, the aptly titled 'Because We Want To' - which, if my memory serves me correctly, she warbled while wearing a short St Trinian's-style school uniform - became the first of her three consecutive number-one hits (she holds the record for being the youngest singer to achieve such a feat).

It was not, she says, much of a wrench to leave her parents and siblings (there are three younger Pipers). She wasn't even particularly homesick. 'I wanted to study and I didn't want to stay where I was. I wanted more. I knew that if I stayed I would end up really resenting my friends and my relationships. I was just very ambitious. I don't know where it came from. I haven't got one of those tragic stories. We didn't have a lot of money, but neither did we wear the same shoes for three years. I just felt like I wanted to express myself quite a lot of the time, and I could do that through art.'

Was the theatre school bitchy?

'I kept my head down, so I didn't see any of that. But it was hard work, and it was lonely at times, because you go from a place where you are the only person with that ambition to one where everybody is like that. It was a tough old life. But it was what you wanted, so you didn't think: "God, I am so tired, I have only had six hours' sleep." You thought: "More! More singing! More dancing! More cabaret!"'

After she became famous, she lived first in a hotel and then, at 16, in a rented flat. The little Pipers needed their parents, so when she toured, she was chaperoned. But the rest of the time, she was rather alone. 'I was living in an adult world and, although I could function in it, I couldn't completely be a part of it.' Her schedule left little time for the business of being a teenager. 'You've got to be on time, make sense, be logical, take care of yourself, make sure you get enough sleep. As a teenager, you're not supposed to do those things. You get out of bed when you feel like it. That was when I felt the sadness of it.'

As for fame, well, once she was smack in the middle of that sandstorm, almost nothing - not even seeing herself on Top of the Pops - seemed to register. 'You don't realise how good things are at the time. It's a weird place to be. It's a shame, but there's no time to sit back and go: "I'm number one!"'

For a while, she was everyone's darling: a squeaky-clean superstar. Then trouble loomed. First, there was Britney, who just seemed so much cooler than Billie. Then the thrill of success began to pale. Billie was still all over the tabloids, only this time the stories were about how troubled she was, how miserable and exhausted. She had a stormy relationship with Ritchie Neville from the boy band 5ive, and she began drinking and 'collapsing' in nightclubs. 'It's not in my nature to throw tantrums,' she says. 'But towards the end, I started to get quite rebellious. I was so tired. I was never a diva; that was just my way of saying I need some control over my life. So I'd go out and get hammered. It sounds more dramatic than it was. It was only once a month.' When did she decide to walk away from it all? 'It was a slow build. I started to get frustrated. Everybody had their hands on me. It didn't work for me in the end. I felt cheated.'

The end came in 2001. At about the same time, she was invited to appear on Chris Evans's Channel 4 show, TFI Friday, and the two of them began seeing one another. To start with, the relationship seemed to follow a familiar pattern. After their first date, Evans sent her a silver Ferrari strewn with roses, in spite of the fact Billie couldn't drive (the car has since been sold, because Piper, bless her, prefers to zoom about in a Clio). It was assumed that the union would be short-lived - that Billie was just another of Chris's crushes, or that the relationship might even be a publicity stunt. There were stories of drunken rows and Billie in tears after Chris visited Stringfellows. They were pictured looking podgy and grey-skinned and down-at-heel. So it was with amazement - and not a little consternation - that the world watched them marry, in May 2001, in a Las Vegas wedding chapel, with no family (unless you count Danny Baker) and no rings, and Billie in a purple sarong and flip-flops.

She likes being a Mrs. 'Yes, I'm used to it now,' she says. 'It's been almost three years.' Was she prepared for the level of disapproval at the age gap between her and her husband? 'I did register that not everyone else might get off on it, but I didn't care at all. When you do things for yourself, it's so exciting! It's so exhilarating. No one can tell you who to marry.' She didn't think twice about going ahead; she always knew she'd end up with someone older. 'We did it because it's too temporary otherwise. It's too easy to walk out if you are not married. And at the time, I was in love. I wanted to be with that person forever. So that's why I went for it. My head is so mad sometimes. When you're young, you have no fear. You don't worry about the consequences. Your philosophy is very much: if it doesn't work out, it doesn't work out. You're not going to die. Some of my friends have been hurt so badly by love that they're quite cynical. I don't have that. I found someone who loved me and I need that.'

She and Evans began married life in high style: they took a little time off - a year, to be precise. They went on holiday, and they hung out in their vast Surrey 'mansion' with their lurchers and their friends down the local pub. They like drinking beer and eating curry (hold the naan!), and are both low-maintenance types when it comes to boring stuff like hair washing. 'I hate shaving my legs and plucking my eyebrows,' she wails. 'I don't care about all that shit. I have gym wear, sleep wear and going-down-the-shops wear, and sometimes I can be in that for days at a time. I think it has to do with having been primped and preened and groomed from the moment I left school.'

Ask her what she loves about her husband's personality, on the other hand, and she is momentarily stumped. 'Everything. He's not like anybody else. He loves life so much. That's a great thing to be around.'

Come on, Billie. You can do better than that. 'Well, we're both ambitious, but not in an ugly way. But it's more the way we see things. Sometimes, I'll see something and if I tell someone else, they're going to laugh at it. Not everyone will understand or think it's important. But we have really great conversations. He's a special boy. I'm mad about him. Everyone should meet him. He's so inspiring.'

Hmm. Unfortunately, a lot of people think he's also a bully and a boor. When he lost his unfair dismissal case against Scottish Media Group, the owners of Virgin Radio, and had to pay more than £7m in compensation, the judge described him as 'manipulative' and a 'petulant prima donna'. I put this to Piper, but she simply affects a kind of wide-eyed shock, as though she is hearing it for the first time. 'I never read anything,' she says. 'I know that it shouldn't upset me, but it would. He's so powerful. They're intimidated, I guess. He's nice: so generous, so cool. Some people can't deal with it.'

And what is it about her that he responds to? After all, before Piper came along, he was - how to put this politely? - all over the shop (one ex-wife, many, many ex-girlfriends). 'Yeah, he was a boy. You'd have to ask him. I've never asked him why he married me. He knows what he likes and what he wants and you just have to trust that. Sometimes, I'll do something that'll surprise him, and it's nice not to know what that might be, because you'll end up playing on that. If someone says: "I really like the way you hold your cigarette", then every time you meet someone new you're going to be hoping you can charm them with your cigarette act. So I don't want to know. Also, it would be embarrassing!' Judging by the look on Billie's chipmunky little face, I'd hazard a guess that this subject is now closed.

My view, which admittedly is one based on only a matter of two hours with the girl, is that - apart from the fact that they clearly fancy one another - Evans probably relishes her compliant enthusiasm for all things Chris. (I doubt she is a nag - you can just tell - and what man, particularly an egotist like him, doesn't want to be adored?) He may also like her strange but very becoming lack of interest in material possessions. Yes, yes, I know it is easy to come over all devil-may-care when your husband has a £50m fortune sitting in the bank. But I get the impression that, even before she was married, she had a very Steady Eddie attitude to cash. The first thing she bought herself after she became famous, for instance, was a wallet. It was Gucci, but it was still only a wallet. 'I've still got it,' she says. 'And I still use it every day. I'm not extravagant at all.

Well, occasionally I have a little binge. This may sound strange, but I went to Whistles the other day and I bought three twinsets. They were a great fit, so I bought in bulk.'

She spends her money on CDs and videos and going out. The only thing she really wants is a souped-up Golf, one with silly spoilers and go-faster stripes. But then, she wonders whether she can't get another year or two out of the Clio first. 'Money's never been a big part of my life. Chris and I never have conversations about money. Maybe we would if we were very poor, but I have so much more fun with people than with assets. That's not to say I'm ungrateful. But the old cliche about it not bringing you happiness is true.'

As for being famous, these days, she tries hard not to notice it. 'I don't have a love for fame. We don't travel with an entourage. I can't see how that would make life enjoyable. I had that as a pop star, and I hated it. I'd rather be in the middle of things than in the VIP room.'

She dislikes vanity of any kind, which is just as well, given her husband's well-documented predilection for a pint. 'I've never been out with a man who has a six-pack. How nice is a man with a belly? Don't you just think that's so sexy?'

I gaze at Piper across the table. She has neatly dispatched her fish, but will be off to have her photograph taken soon, because coffee is a problem - we are in a French establishment and they do not have the necessary soya milk. She still looks as composed as a waxwork model, but seems oddly out of place, at one remove - an effect only heightened by her weird tendency to refer to the real world, the one you and I inhabit, as if it is a country she has not visited for many a year. ('From what I hear, the pace of life is faster than it's ever been,' she says.) Does she feel young or old for her age? 'Not old exactly, but when I get together with friends I see a difference in our personalities. Sometimes I get angry with myself that I've done too much, that I haven't saved anything. I mean, what could possibly make me excited?'

Ever the stage-school girl, Billie is smiling brightly as she makes this final confession. But still, it sounds pretty tinny to me - as sad and as empty as anything I have ever heard.

Source: The Observer