Her victory on X Factor saw the nation fall in love with this strikingly beautiful and powerful-voiced singer.

But Leona Lewis would have been a star anyway – with or without the TV talent show.

“I have always known what I wanted to do – and that is to sing,” she says, talking to me before a show at the start of her new tour.

“It is one of the things I am positive about and I have done it since I was a youngster, so it’s good people are listening now.”

And millions of us have been doing just that, since the unknown, classically trained opera-loving singer and BRIT school graduate from Hackney first wowed television audiences six years ago, showcasing her expansive vocal range with emotion-drenched ballads.

Sales of her debut album Spirit reached eight million copies, while the lead track Bleeding Love saw her topping the charts in more than 30 countries – occupying the number one position in the UK for seven weeks, and going to the top of the American charts, making her the first British woman to do so since Sheena Easton in 1982.

She has gone on to sell 20 million records around the world, racking up nine UK top 10 hits, scaling the album charts with number one follow-up Echo, and last year releasing her third album, Glassheart, which she is now taking on the road. “X Factor has definitely given me a huge stepping stone,” she says. “Having my video go viral gave me a global audience. But I was doing this before X Factor and would have kept going anyway. There’s no way of knowing how it would have gone, but I’d still be doing what I’m doing now.”

The tour reaches Oxford on Sunday, and, like her 2010 Labyrinth tour, it sees Leona do more than just sing. The show has a narrative, she says, telling a story designed to gladden the most jaded of hearts. “It has a joyous theme about getting your heart broken but then things coming back together again,” she says, dreamily. “The story is important and there has always been that side to my performances. It’s not just music; there is something that requires you to think a bit about what’s going on. It’s very honest.”

And, she says, fans may be in for a surprise. “My new songs have got a different flavour because of the different producers I’ve been working with,” she says. “There’s a bit of dubstep in there and some songs reminiscent of the ‘80s, which are really cool. But while I’ve evolved a bit, it’s still me.”

And, says the down-to-earth Londoner, it is going down well with fans. “The audiences have already been really supportive and are reacting to it. And it’s nice to be doing it on my home turf.

“People are standing up and singing, which gives the shows such great energy.”

It is no secret that far from being a vacuous product of primetime TV, Leona is a woman of strong principles. She’s a committed vegetarian and an anti-fur campaigner. She once turned down a large sum (she declines to say exactly how much, though insists it was less than the million pounds reported elsewhere) to open the Harrods sale because the shop continues to stock animal fur products.

She has also launched her own ethically sourced clothing line through Top Shop and has her own fashion company.

“I’m as passionate about these issues as about my music,” she says. “And it’s good I’m able to do this.”

So, after six years of stardom, what does Leona enjoy the most? “I have loved the travelling,” she says. “I still love going around meeting people – here, or in Germany, New York or Los Angeles.”

It hasn’t all been easy though for this modest hard-working girl. “It was difficult at first,” she says. “If I went out I’d have to stay with someone as people would come up to me all the time which was overwhelming.”

And while adapting to celebrity, she still comes across as a softly-spoken, endearingly old-fashioned girl, who remains close to her family and old friends. “They are the main thing in my life,” she says. “I am close to my mum and dad and they try to come to every one of my shows. They’ll even be in Oxford.”

Does she, I ask, ever hanker to return to her classical roots? Perhaps the time is right for an opera album? She laughs. “Yes for sure,” she says. “I love classical music and have always said I’d love to do an opera album. “Classical music has a diminishing audience which is sad as it’s so amazing. I really liked it when I was younger too as it’s all about storytelling, and people have lost that in music.

“With me, it’s all about the story!”

So how about ‘Leona Lewis the Opera’... the story of the girl who rose from humble beginnings in Hackney to take on the world? “It could make an opera!”she laughs. “I’m proud of what I’ve done,” she goes on. “It’s good that I’ve done a show like X Factor and am able to sustain a career to carry on doing this. I always said I wanted to be a recording artist as soon as I left school, and I have been able to achieve that. “I really enjoy what I do and just can’t wait to get on that stage – and have a good time.”