Simon Cowell is on speed dial and Beyoncé is her biggest fan, but despite being The X Factor's most stratospheric star, Leona Lewis has, so far, managed to keep her feet on the ground. Since triumphing in 2006 she's had a smash-hit debut album, a No1 in America, appeared on stage with Justin Timberlake… the list goes on. Not bad for a girl from Hackney.

But despite the fame and accolades, Leona remains remarkably unfazed. She still lives in the same borough of east London, parties with the same friends and dates the same boy she's known since she was 10.

"It's what keeps me grounded," she admits. "I make sure I have plenty of time chilling out, doing normal things. You know, having lie-ins, catching up on EastEnders."

It sounds like a record company line. But when you spend time chatting to Leona – who has a reported personal fortune of £6million – it's impossible not to believe she's the real deal. She's so down to earth. Almost scarily so, given her meteoric rise to superstardom.

Her first album Spirit went straight to No1 and was the fastest-selling UK debut album of all time, shifting over one million copies. She topped the US charts with her single Bleeding Love, and became the only British woman in 20 years to reach No1 in the US album chart. All this in less than two years.

Of course, there have been the invitations to move to LA and live life in the fast lane. But the 23 year old genuinely does appear to prefer Hackney, and the same two-bed house she lived in before the show.

Although there was that rumour about Simon Cowell stumping up the cash for a mansion in Los Angeles – far more befitting of a global superstar.

"That was hilarious," she says. "People kept asking me about the house. I was like: ‘What house?' At least I could say to Simon: ‘Er, so where's this house, then?'"

The house may have been imaginary, but there are other spoils of life as an A-lister.

"I always think that I should eBay the handbags I'm sent," she jokes.

But it's when she explains what she really does with the gifts lavished on her that you begin to understand what Leona's truly like.

Take the designer arm candy, for example. Leona's been a committed veggie since she was 12, so if the freebie handbags she's given are leather, she won't even contemplate using them.

"They either get sent back, or I give them to family," she says.

Even a Burberry, which most girls would gladly fight to the death for, wasn't allowed to grace Leona's arm, and when Harrods offered her £1million to appear at the store, she declined because it stocks fur items.

"I can't let go of my morals," she says. "Even for £1million."

Other temptations seem to pass her by too. Unlike fellow BRIT School pupil Amy Winehouse, Leona says she doesn't like the taste of alcohol, and that she's "not the sort of person to come stumbling out of nightclubs. My dad would go mad if I did that!" A scandal-free star? We bet Mr Cowell is chuffed.

Her love for electrician boyfriend Lou Al-Chamaa, also 23, hasn't wavered since she hit the big time either.

"I love my boy and that he's out grafting and earning his way. I really respect that. He's not interested in the money," she says.

It's the same with her friends. Neither her gal pals nor the places they hang out have changed.

"Oh God no, we're exactly the same. They never expect me to pay for things. They're all such independent girls," she laughs. "Nothing's changed at all."

And yet… how can it not have? There's no hiding from the fact that Leona is now an international superstar who flies on private jets and hobnobs with celeb royalty. Everyone wants a piece of this girl. Roberto Cavalli designed her dress for the BRITs, and even uber-diva Beyoncé didn't hold back.

"I met her at a concert we did together," says Leona. "It was incredible. She said she was a huge fan – I was blown away."

Which is typical of Leona. Despite the parties, money and adoration, she never takes her success for granted. Let's hope it lasts.

Leona's single Forgive Me is out on November 3. Her album Spirit – The Deluxe Edition is released on November 17.

Is The X Factor a good way to launch a singing career? What do you think of the ‘manufactured’ bands that seem to be around these days? Is it enough just to have a good voice or do you need a great management team behind you?

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PHOTOGRAPHY: REX, ITV, MATRIX