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Just like the sticker on her CD says, the wait is over. Forty minutes behind schedule, Leona Lewis ambles into the fifth floor room of a private members' club in East London and asks the waitress for a glass of “children's apple juice”. She sings like a diva and - bereft of context - these details alone might tell you that The X Factor's most successful gift to the pop world is beginning to act like one.

But the difference in juices is substantive. As the waitress explains, the adult juice is cloudy and greenish; the kids' version pink and sweeter. And if she's late, well... given that she was in Berlin five hours ago, and Italy the day before that, she's done well to get here at all. Last night she appeared on the German equivalent of the long-expired Matthew Kelly gameshow You Bet! “One of the contestants was this guy running backwards and jumping over hurdles,” she says. “I think it would have been funny if they had got me to jump over hurdles with my heels on.” Lewis peers up at where the thought bubble depicting such a thing might be and giggles. Within five minutes of meeting her it's already apparent that a newly sculpted snowman would feel a little grubby next to her.

And with good reason. Had she wanted to, Leona could have had a lie-in, but it's Mother's Day and she elected to wake at 3am because she promised her mum that they would do lunch together in town. You would have thought that West End shopping trips might have become problematic by now. But Lewis says that sometimes entire days go by without her being recognised. “People can be like, ‘Oh, can I get a little photo?' or ‘Well done' - and there'll be some people who shout your name from across the street.” Well, it's not that Leona doesn't like the latter - more that she doesn't quite know how to deal with them. “You're like, ‘OK, um... hi!'”

But she insists that it's a small price to pay for a scale of success that has eluded previous Pop Idol and X Factor winners such as Michelle McManus and Steve Brookstein. From the outset it was clear to everyone - with the possible exception of Lewis - that a voice like hers was worthy of greater things than its prime-time predecessors. As a guesting Gary Barlow said to Simon Cowell, “This girl is 50 times better than any other contestant you have ever had, so you have a big responsibility to make the right record for her.”

If there was a subtext to the Take That singer's comments, it was clear in Cowell's squirming reaction. Cowell - past master of making a fast buck out of talent show winners - could be trusted to make the right record for Simon Cowell. But after bagging the best-selling single of 2006 with A Moment Like This, could Cowell make the most of Lewis's long-term prospects? The critical consensus on last year's debut album Spirit was that Lewis had played it too safe. What she had in her favour was the endorsement of a bigger, more experienced mogul. Enter Clive Davis, the man who discovered Whitney Houston and Alicia Keys. He was quick to throw his weight behind Lewis and ensured that she was the first X Factor winner to secure a deal on both sides of the Atlantic. Davis's involvement, says Lewis, gave her access to the best songwriters - “and that's why I did a showcase with him... to work with the best people. Clive has that respect.”

In commercial terms, at least, the gamble to hold back from a quickly recorded cash-in has paid off. There are some ace songs on Spirit - in particular the machine-tooled Europop melancholy of Take a Bow and, of course, last year's monster chart-topper Bleeding Love. Given the right songs, Leona seems incapable of disappointing. But a question mark remains over Cowell's fondness for mawkish sub-Céline mush like her new single Footsteps in the Sand - an adaptation of the allegorical Christian poem, which now boasts a Cowell co-writing credit. What exactly did he do on it, anyway?

“He came up with the original idea to make it into a song,” explains Lewis. He told me [about it] and I was, like, ‘That could be really quite interesting.'”

So, he gets songwriting royalties just for coming up with the idea of putting it to music?

“Yeah! He does,” she says brightly, before registering the look of utter disbelief on my face. “I know!”

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