Does Leona Lewis ever get fed up with being viewed as some kind of "anti-Amy Winehouse"? Maybe it is because they both attended the performing arts BRIT school in Croydon, but it seems, especially in Britain, Lewis and Winehouse are forever linked in the media eye as polar opposites.

And while Winehouse doesn't exactly get an easy ride, Lewis, 24, is often saddled with a drippy persona quite at odds with her achievements: winning The X Factor, topping the chart with "Bleeding Love" in more than 30 countries, being the first Briton to get to number one in the US with her debut album (Spirit), singing at Nelson Mandela's birthday concert and at the Beijing Olympics… the list sprawls on.

Nor does this "soft" image tally with her widely publicised decision to turn down a lucrative appearance at Harrods (an animal lover and vegetarian since the age of 12, Lewis objected to its fur hall). If that doesn't grab you, she also asked Jimmy Page of Led Zeppelin if he would mind changing "Whole Lotta Love" to suit her voice for the Beijing ceremony (I know grown men who would faint if they met Page, never mind request he amend his chord changes!)

Indeed, all the evidence points to a thread of steel running through Leona Lewis that enables her politely, but very firmly, to get to where she wants to in life.

Then, of course, there is her voice – that big, beautiful, bruised one-of-a-kind voice that convinced Clive Davis (who discovered Whitney Houston) to represent Lewis in America within seconds of hearing her. The uber-vulnerable tone which has become her trademark, and which, when I ask her where it comes from, Lewis slightly struggles to explain.

"Its about the emotions in the lyrics," she says tentatively. "Just from this really raw emotional place, you know, from real stuff that I've gone through." Does it always have to feel real to her? "Yes," says Lewis, suddenly decisive. "If it's not genuine, it's a waste of time – it's not going to come across. No one is going to believe you."

We meet in a London hotel. When I arrive, Lewis is sitting on a sofa. She is young-girl stylish, rather than diva-styled, her signature caramel curls framing her long, thoughtful, pretty face. When I ask if Lewis feels more beautiful since she became famous, she is astonished. "If anything I feel more 'ugh!' Sometimes I think I want to get 'hair and make up' every day, but that's just not possible."

On the sofa next to her is Dreams, her recently published illustrated autobiography, a kind of scribble book of informal photographs and thoughts (Leona smiling on horseback, Leona in hotel room, Leona with rollers in, etc). Lewis also has a single coming out: the bittersweet "Happy". This will be followed by her second album, Echo, for which she wrote most of the tracks, flying back and forth between London and a "second home" in LA to record it.

Lewis tells me she is both excited and nervous about Echo, feeling that "everything is stepping up a level". For someone who sings so big, her speaking voice is incongruously delicate, sometimes trailing away altogether. Still, she seems assured enough, occasionally using her long, expressive hands to emphasise points.

When she read through some of her old press did she recognise herself? "You mean, people saying I was shy and nervous? Yeah," smiles Lewis. "But I don't think I was that shy, I was more reserved and quiet. It's just the way I am. It takes me a while to come out of myself, and get to know people."

It's interesting, I say, that so many descriptions of her implied weakness or frailty, when her achievements suggest quite the opposite. "Sometimes it did seem exaggerated," she agrees, "because I am very strong in lots of ways. I'm very strong creatively, in my music. I'm very strong about the decisions I make, my ethical beliefs, and what I stand for."

So why does she think people get the wrong impression? Lewis shrugs. "I think when people see that you are shy, or even just calm, collected and reserved, they think you can be pushed around, made to do everything they want – but that's definitely not true of me. The people closest to me know that's not the case." Lewis's eyes glint slightly: "They know I'm not a pushover."

Lewis was raised in Hackney, east London, by her father Joe, a youth offending officer and a DJ of Guyanese descent, and her Welsh-bred mother Maria, a ballet teacher-turned-social worker, along with her brothers, Bradley and Kyle. There are pictures of them in Dreams – an attractive, vibrant-looking family. There was a tragedy when Leona's cousin, Billie, died of leukaemia aged 14, which Lewis says she prefers not to speak about for fear of wounding family members. "For anyone who loses someone it's devastating, hard to get over." All in all she feels she had a great upbringing. "I was very protected by my parents, and I felt very safe."

After she became successful, Leona bought the Hackney flat she rented with boyfriend, Lou Al-Chamaa, so she could be close to her family. She still loves the area's "cultural melting pot", while being saddened by the poverty and lack of opportunity. When I ask if there is an element of guilt – because she "escaped", as it were – Leona is surprised: "No, because I don't think it was ever meant as an escape."

Lewis's musical heroes were Minnie Ripperton, Eva Cassidy and Stevie Wonder. Realising their daughter loved to sing, her parents sent her to the Sylvia Young and Italia Conti theatre schools, until they couldn't afford it any more. Later, she attended the BRIT school, leaving at 17, to "get out there". She was already writing and recording, working variously as a receptionist and a pizza waitress, when Al-Chamaa suggested she audition for The X Factor.

The X Factor made Lewis's name, but she could be forgiven for inwardly groaning every time it's mentioned, though she swears she doesn't. However (the little thread of steel again), Lewis is convinced that, with or without The X Factor, she would have "made her path anyway".

Really? Gifted though she is, the music world is full of wonderful session singers, desperate for a break. "True," says Leona, softly. "But I still like to believe that, being dedicated and working hard, I would have done it, that you can still do it that way. The thing is, with music, because I loved it, and my family loved it, because it was so natural to me, I was never going to give up, it was just there in my everyday life."

Lewis doesn't think last year's winner, Alexandra Burke, is that similar in style to her, though she was pleased a girl won. What about Simon Cowell – where is he positioned in her life? The answer seems to be: friend, mentor, label boss… all very complicated. Does Lewis find it amusing that people view Cowell as "mean"? "Yeah," she says, "because I don't see that side to him, except on TV. We're quite similar, I think. He's quite a shy person, actually." Shy? "Yeah, his facade is a mean exterior, but he's not like that really."

Lewis feels that one reason Cowell makes a fuss of her is that she was his first female artist in 20 years. Perhaps he's relieved she isn't a nightmare diva-type. Has Lewis ever felt like throwing a tantrum, just for the hell of it? "It would be funny to do that one day," she smiles. "It would be so… not me."

There are some who see this "not me" business as a problem with Lewis. As if the combined effect of The X Factor, the ongoing rumours about Cowell being ultra-controlling with his acts, and her not being a demanding pain in the neck means she must lack credibility.

Does it get to her, this credibility issue? Lewis insists not – not even after the notorious rumpus when she ended up being feted at the Grammys, but overlooked at the Brit Awards (she says she was thrilled as a newcomer even to be nominated). Where Cowell being controlling is concerned she maintains he has listened to her all along, most notably when she suggested "Bleeding Love" for a single. "I know I didn't come out of a cookie-cutter machine," she says. "As I keep doing my music, I think people will see that. I hope I'll be able to prove it to people, anyway."

What about the celebrity side of things? At first, says Lewis, it felt "alien and strange. I know it sounds a bit naïve, but I never really thought of fame, I only thought that I would sing onstage and it would be lovely." She is finding her feet with it now: "I think some people love fame, some people hate it, and some people just go along with it, and I think that's what I do, I just kind of go along with it."

Does Lewis believe in the "Faustian pact" theory of fame – people opening doors, not realising they can't close them again? "I think people probably get themselves into situations where they try to close it off. But once it's happened, and you've let it in, that's that. And for that reason, I never will." How does she think she'd cope with "extreme celebrity"? "I'd go nuts. It would be horrible. I feel so sorry for people who have it that bad. That's probably why I keep such a low profile because once that line is crossed, you can't stop it; you can't say, 'I don't want this any more.'"

One supposes Winehouse would be an obvious example. "I don't know Amy personally," says Lewis carefully. "But, honestly, she's just living her life. When you're not in the spotlight you can do that – when you're not having pictures taken, you're not living your life in front of everyone. I feel bad that everyone is involved with every single part of her life, and she hasn't got time to recuperate, to just be away from it."

One thing I've noticed in Lewis's press is a kind of snide bewilderment that she is still with her electrician boyfriend, Al-Chamaa, who she's known all her life, and been with since she was 17. Does Lewis find this offensive? Her eyes flash. "I find it very offensive. It's offensive to him – implying he's not good enough for you any more – but also to you – saying you're so shallow you'd dump him when you became successful? "Yeah," says Lewis, "It's like, seriously? This is real life, it isn't make-believe. For people to think that you should leave someone because, all of a sudden, you're a singer and you have opportunities. I feel very sorry for them.

"It does make me angry," she continues. "Because he's a great person. And it doesn't matter what you do in life, what your job is, where you come from. None of that matters to me, what matters is who you are as a person – nothing else."

You are extremely close? "We are best friends." Are you the kind of person who doesn't fall for the myth of tempestuous, unpredictable relationships being more "real" or valuable? You cherish the stable, the solid, the good? "Yeah, I feel like that in love, and all my relationships in general. I feel that all really strong relationships are based on trust. All my friends I've known since I was really little. It's not that I don't let new people in but I do feel…" Leona searches for the right word "safe with people that really know me, who know who I am."

I find it intriguing and rather heart-warming that of all the things guaranteed to make Leona Lewis's eyes flash, it is the thought of anyone rubbishing her boyfriend. Clearly she wasn't kidding about not being a pushover. It also seems to be part of the same unshakeable moral code, the sense of knowing exactly who she is, that gives Lewis the strength to cope with anything, from suggesting a rock idol change a track, to turning down Harrods.

What about being a "woman of colour" in the music industry? Didn't soul singer Estelle say it was so hard for black artists here, she ended up having to go to the States to make it?

"It's difficult," says Lewis thoughtfully. "Because I haven't experienced it like Estelle has. It's hard for me to identify with – 'You're this' or 'You're that.' Because I'm not, I'm mixed race. So it's not like I'm [puts a fist up], 'Power!' But, at the same time, I am from an ethnic background, I am mixed."

Lewis thinks there should be more women in the music industry generally – "Not just singers: A&R women, producers, engineers." She holds up a long, slender finger. "I've come across one female engineer, no female producers. It's such a male-dominated industry. My manager (Nicola Carson) is really cool. She's setting up nights where women in the industry come together, empowering women. I think that's great. Otherwise, it's just all men: management are men, everyone in your record company is a man, and it's not good."

You sound quite feminist, Leona.

She laughs shyly. "Some people could say that. I am a little bit. I definitely believe in female empowerment."

The interview is coming to an end. Lewis and I chat a bit about the non-leather line of bags, and other accessories that she is thinking of developing with Philip Green of Topshop. Its clear that Leona loves animals – does she like children, too, to the point of some day having any of her own?

She wrinkles her nose: "In the future definitely, but not within five years. I can see myself being an older mum. But I probably haven't given it proper thought as it's so far in the distance. I am a family person. But I say that and I am career driven as well! It's like 50-50."

One last question. Because of the title of the single, everyone is going to be asking Leona if she is happy. So is she?

"Am I happy?" she grins. "Yes. Some bits have been hard, but it's everything I thought it would be and more."

And if it all ended tomorrow?

'I would probably go and sit on a farm with loads of horses and all kinds of animals. That's truthfully what I would do. Be a horse lady, learn to give lessons, stuff like that." Lewis is quite adamant. "That's how it will be. You will find me on my farm. You really will."

When I get home, I flick through Dreams. The pay-off line is: "Don't limit yourself. Dream Big." There's a lot to like about Lewis, from her voice, to her attitude, to her New York-LA-Paris-Hackney vibe. And for all her liking of the word "safe", in her own quiet way, she is not averse to taking a few risks.

The next time I get to speak to Lewis it is on the phone. It is some time before the horrible incident during a book signing for Dreams, at which she was punched on the side of her head by a "disturbed fan". Talk about the extremes of celebrity! It seems to say it all about Lewis that one's immediate thought was "Unfair. Why her?" Al-Chamaa is reported to have instantly rushed forward to protect her.

Both of us blissfully unaware that any of this is in Lewis's future, we chat on a very crackly line that almost drowns her tiny speaking voice. A couple of days earlier, Cowell had held his 50th birthday party where Leona had sung, but if I thought I was going to get any party gossip about risqué speeches and sloshed A-listers, I am bitterly disappointed.

Lewis tells me that she'd flown back for the party from shooting a video in Cuba: "I literally ran onstage, sang, and then went home." She didn't stay for any of the festivities? "I couldn't stay. I was the walking dead."

Her itinerary for the foreseeable future doesn't sound any less tiring, taking in trips to France, Sweden, then over to LA, back to London… you get the drift. By anybody's standards, a lot to handle.

Lewis has said that she gets her dreaminess from her mother, her drive from her father. But where does she get her preternatural maturity, her self-possession to handle all this? She tells me that she's always been mature. 'I've always had friends who are a lot older than me," she says. "Always been mature like that. I think that's why I left school at 17 – because I knew exactly what I wanted. That's the thing about me," says Lewis, just audible over the crackly line. "If I set my heart on something I can't let it go."★

Leona's new single, "Happy", is out on 9 November on Syco. Leona: Dreams is published by Hodder & Stoughton, at £20. To order a copy for £18, with free UK p&p, go to guardian.co.uk/bookshop or call 0330 333 6847