THE streets of Islington are today adorned with posters urging people to support their new local hero, Alexandra Burke, the 20-year-old who stands on the brink not only of winning tomorrow's X Factor final but also of superstardom.

Not many people know this, but just a few months ago, you could have paid Alexandra a mere £200 to sing with her band Soul Explosion at a wedding or bar mitzvah where she specialised in belting out their "full Jewish repertoire" including classics such as Hava Nagila.

But after Saturday night, when she will sing before an anticipated ITV audience of 13 million people and attempt to beat rivals Eoghan Quigg and boy-band JLS to a £1 million recording contract with Simon Cowell, the sky is the limit.

What an incredible journey it has been. Brought up by a single parent in an Islington housing association maisonette, she was first inspired to go on stage by her mother, Melissa Bell, a feisty soul singer who has since suffered kidney failure because of diabetes and fallen on hard times.

"There was a period in the Nineties when I toured the world with my band Soul II Soul and earned £250,000 a year performing with George Michael, Liza Minnelli, Queen, The Who, Elton John and Stevie Wonder," says Melissa, "but now my health is poor and I'm lucky to scrape £20,000 a year."

Melissa, 44, has just returned from dialysis at the Royal Free Hospital and sits bent over and short of breath on the sofa surrounded by her three other children, Sheniece, 22, a trainee beauty therapist, David Jr, 21, a budding accountant, and Aaron, 16, who is still at school. Three times a week, while her daughter is being groomed as the next Whitney Houston, Melissa goes for life-saving treatment, all the while waiting for a new kidney matching her rare blood type.

There is something appealingly relaxed about the Burkes: it is mid-afternoon and yet a family friend wafts about in her pyjamas, neighbours breeze in and out, and Sheniece chats on the phone while messaging friends on Facebook. It feels as if I have stumbled onto the set of East- Enders. Yet the air is tinged with pride.

For when I ask who was Alexandra's biggest influence, Melissa rouses herself, suddenly reinvigorated. "I was!" she says fiercely. "One day, when she was nine, I was doing a corporate gig in front of 400 people and Alex got up out of the audience, walked up to the stage and said: 'Mum, can I sing?'

"She took the mic and sang Coco Jumbo, a popular dance song, and the audience loved it. She had a kind of mesmerising star quality, even then. That was the first time I thought: 'Wow, she could really make a go of this.'

"After that, she took every opportunity to come to the recording studios and she did backing vocals on many of my tracks."

But Melissa's growing success with Soul II Soul, a band that won two Grammy Awards and sold more than 100,000 albums, would take her away from her family for up to a month at a time. As Alexandra's father, David, a restaurateur, had walked out on the family when she was six, she was left in the care of her granddad, Ivan, and childminder Pauline Harty, whom Alexandra called her "second mother" and who, as we shall see, played a key part in her decision to enter this year's X Factor.

When Alexandra started secondary school at Elizabeth Garrett Anderson School, an all-girl comprehensive in Barnsbury, and came under the influence of the head of music, Sarah Beagley, her voice began to develop. "I will never forget the first time I heard Alexandra sing before an audience," recalls Sarah, 40. "She was just 11 and she entered our talent competition and was up against 24 other girls, some of them 16 years old.

"As she opened her mouth to sing You Might Need Somebody by Shola Ama, a chill went up my spine. She had such a powerful voice and such a deep, resonant sound that I looked at my fellow judges and I could tell we were all thinking the same thing: she's only 11! She blew us away. When she finished, the pupils rose to their feet and gave her a thunderous ovation. She won, which was some achievement given that we were a school renowned for its performing arts."

For the next five years, Sarah, assisted by voice coach Alison Campbell, worked on moulding Alexandra's raw talent. "We taught her keyboard skills, how to read music, how to broaden her range, and most importantly, we developed her breathing technique so she could sing technically correctly and not damage her vocal cords. She was a model student: always on time, well prepared, and incredibly self-assured in a modest way. She had a three-octave range, which is pretty handy, and in the school choir she could sing low alto to top soprano.

"One year the choir was asked to provide support for the internationally-acclaimed opera singer, Sir Willard White, who was performing the oratorio El Nino at the Barbican. White was known for his big, rich baritone voice but during rehearsals, he turned to me and said: 'Who's that girl with the big voice? She's going to be a star.' "

By then, Alexandra, still only 12, had entered the TV show, Star For A Night. She reached the final only to lose to Joss Stone, who is now a close friend.

Does Sarah regard Alexandra as her protégé? "No," she says. "Although we still keep in touch and I am immensely proud of her, it's her mum who has been her most profound influence.

"Having said that, the driving force in Alex's life has always been Alex herself. By the time she left school at 16 after completing her GCSEs, she'd gone from a little girl with a big voice to somebody with star quality."

Not everybody thought she was the finished article. In 2005, Alexandra, then 16, auditioned for X Factor and, having got through to the Judges' House stage, failed to make the final 12 when mentor Louis Walsh sent her packing because she was "too young". At the time, a devastated Alexandra blasted him on GMTV. "Why invite 16-year-olds onto the show if they're all going to get kicked out simply because of their age?" she said.

Sarah thinks Louis "made the mistake of his life for letting Alex slip through his fingers" but Melissa takes a different view. "Louis didn't screw up," she says. "Actually he did her a favour. She wasn't ready. She needed to go away and work at her craft, which she did."

Yet, incredibly, Alexandra would probably still be blazing a path through the wedding and bar mitzvah circuit were it not for the nagging persistence of her "second mum", Pauline Harty, who begged her to give X Factor another shot. When Pauline died of lung cancer in March, Alexandra sang at her funeral and resolved to honour her request. And it has helped, too, Melissa says, that this year Alex made up with her father who has re-entered her life.

If, as Simon Cowell and her mentor Cheryl Cole expect, Alexandra wins X Factor, what will it mean to the family? "My bank account is down to just £124 so I hope Alexandra will lend me a tenner," chuckles Melissa. "Actually, some people think we must be rich because of my success with Soul II Soul, but we're not. Anyway, it's not about the money. It's about getting a recording contract and living the dream of a successful career in the music industry.

"Also, I think it means something for Islington. This borough has not had a good year with all the knife crime. Ben Kinsella [the 17th of 28 teenagers to be murdered in London this year] lived nearby and was a friend of the family. It's great that Alexandra is putting the borough on the map for all the right reasons."

Melissa says she talks to her daughter twice a day and that Alex is feeling upbeat. What advice has she given her? "Be yourself, do your best, the rest is up to God. I'm incredibly hopeful.

"I went with Alex to the first auditions at the Emirates Stadium and as she was being interviewed by the host, Dermot O'Leary, I watched her sitting there among the hundreds of contestants looking so demure and mature. I collared Dermot's private runner and said: 'Excuse me. Do you see that girl being interviewed by Dermot? She's your winner. Her name's Alexandra Burke. I want you to remember this moment and when she wins, I want you to call and apologise for looking at me like I'm completely crazy.'

"On Saturday night I'm going to find that guy just to see his face. But whatever happens, Alexandra's life will never be the same again. The world is about to find out what a phenomenal singer she is, a kid who had the guts to face defeat and try again, and who, I believe, has the X Factor and so, so much more."

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