LONDON ? Rapper Speech Debelle scored a surprise upset Tuesday by winning Britain's prestigious Mercury Prize, beating favourite Florence and the Machine and chart-selling rock act Kasabian.

Debelle won the 20,000-pound (?22,700, $33,000) award for her debut album "Speech Therapy", which was inspired by her troubled south London upbringing, including a spell of homelessness.

"I feel so good. It feels better than I imagined. My family's here. My friends are here. I'm from south London -- I don't get emotional -- I'm emotional," the artist said at a ceremony in London.

"This proves if you believe in something and you think you can do it, you can achieve it."

Debelle, 25, spent time living in a hostel after her parents asked her to leave home after a troubled period as a teenager.

"She's just quietly telling her stories in the most beguiling way," Mercury judge, broadcaster and conductor Charles Hazlewood said.

Her album has not sold enough copies to reach the Official UK Albums Chart -- having sold fewer than 3,000 copies since its release in June -- but the win in almost certain to spark a surge in sales.

Debelle, whose real name is Corynne Elliot, said her win was proof that there was room for originality in music.

"There's a lot of music that sounds the same, all day on the radio, and my album don't sound like their album and it's still won the Mercury Prize," she said.

"Hopefully this will throw a wrench in the system and people will hear this album and realize they don't have to make music that sounds the same - they can make music that sounds good."

Florence and the Machine -- starring fellow female singer Florence Welch -- had been the bookmakers' favorite ahead of the ceremony, while Bat For Lashes -- singer-songwriter Natasha Khan -- was also highly fancied.

The Mercury Prize is awarded for the best British or Irish album of any genre released in the year to July.

Organisers claim it is Europe's top arts award in terms of influence and media coverage. The prize is known for representing an eclectic range of styles, but usually leans towards indie and rock music.

Debelle, who was chosen by an independent panel of judges, joins an exclusive club of past winners including Arctic Monkeys, Portishead, Pulp and Franz Ferdinand. Manchester band Elbow won last year's award.