First Night: Speech Debelle, Scala, London

Worthy winner comes home with bubbles with joy

"Look at you all!" says Speech Debelle, looking out at a fairly full house of white-heeled white, and some black, bohemians. "See what the Mercury can do!"

This is the 23-year-old south Londoner's first big hometown gig since her Mercury Prize win last month with her debut album, Speech Therapy. The insupportable implication that it's 2009's best British LP has made some think the Mercury has lost its way, but don't blame that on Speech.

Her support act, Kasha, rests himself on such shifting sands when he insists his rap "Wildhearts" is: "a true story ... if you have a heart you will be touched." Actually, there are no moments in his set or Debelle's when I feel touched by the tough lives both express. The delivery doesn't put that hurt over, and Debelle doesn't even try. Lived or observed, her lyrics are both horribly blunt and humanely warm. But these days, she is having the authentic time of her life. Her girlish voice bubbles with joy, not pain.

The trio backing her – double-bass, acoustic guitar and drums – emphasise this isn't hip-hop, but rapped jazz. Race doesn't define her, either, when Glasvegas's white working-class Scot James Allan articulates themes of absconding fathers and destructive violence with greater force. You might compare her to Dizzee Rascal. But only in the way he has used early trials not as weights to hobble his future, but fuel to fly into new experiences. "This one goes out to all my people with ambition," Debelle shouts in that spirit, during "Finish This Album". "I'm gonna represent the youth ... eat more fruit," she adds, spokeswoman for a generation aspirations wisely undercut. She'll fix the world when she can stay out of the fridge.

Debelle already looks grateful for her homeless years, and has lost interest in "Daddy's Little Girl", her most furious and vengeful song to the past. Her signature song, "Searching", begins "2am in my hostel bed", and, if you listen hard tonight, includes her harshest lines: "I know the blair witch I seen her yesterday, she collapsed naked in her bed with a needle in her crotches." But it is delivered not from the floor of a crack den, but with the ebullience of someone far from there. "I've got more lies on my CVs than pros have STDs" she brags of grinding 9-to-5 days now also vanishing behind her. Instead, she hurls herself hardest into "Go Then Bye"'s pop song of a young love affair's ordinary end.

Court cases are for the men in her songs, half-wanted babies for the girls. But Debelle's biggest problem these days is "having to look good all day now". The paparazzi, and many Mercury-drawn fans, may soon leave her performance-poet jazz to its natural, tiny constituency. But Speech Debelle the woman remains a worthy winner.