It was only a matter of time before the backlash started. Ms Dynamite had barely had a chance to figure out how she is going to spend the £20,000 she won this week as the first black woman to win the Mercury Music prize (she's giving it to charity) when accusations of "selling out" and her music being too "soft" began to be bandied about. How predictable. In some ways it is fitting that such a British talent should be criticised in such a British way - after all, as a nation we love nothing more than to build people up, only to tell them they've got too big for their boots, or in this case trainers. But the criticism levelled at Ms Dynamite is a little deeper, as she would say. Word has it that you could practically hear the (largely white) music establishment breathe a sigh of relief when she arrived on the scene. At last, here was a black, British female musician who sang songs that criticised the threatening gangsta machismo of male rap. Quick, give her an award.

But Ms Dynamite - Niomi McLean-Daley to her mates - is not an ordinary British talent, and as such she deserves more than such lazy commentary. There is nothing soft about her music. Look beyond the sweet voice and you'll hear that her lyrics are as powerful as she is pretty. In the single It Takes More, for example, she criticises the blatant hypocrisy of rap and R&B's obsession with diamonds and the "bling bling" ghetto-fabulous swagger of the likes of P Diddy. With lyrics such as "Now who gives a damn/ About the ice on your hand?/ If it's not too complex/ Tell me how many Africans died/ For the buggettes on your Rolex", it is clear that this is a woman who is unafraid to say what she feels, no matter how many influential noses she puts out of joint. Even the fact that she has gone for "Ms" rather than "Miss" is notable, and proves that she is not afraid of making a statement.

Daley is, if anything, all the more remarkable considering where she has come from. Born in Archway, north London, one of 11 children of a Scottish mother and Jamaican father, she grew up without a lot of cash and caring for her younger siblings. But she has nine GCSEs and three A-levels and was planning to read social anthropology at Sussex University before she fell into music. And she is still only 21. Little wonder that industry insiders are impressed.

"She operates on a different level from any other well-known female rapper," says George Ergatoudis, music manager for 1Xtra, the BBCs new radio station for black music. "She's much more connected with the honesty of modern street life. The American female rappers are all talking about the same issues that obsess male rappers: sex, money and fashion. They've got a lot less to say. They might make good music, but in terms of lyrics Ms Dynamite wins hands down."

"It's the realism of her," says Radio 1 DJ Trevor Nelson, one of the most influential figures in British black music. "It Takes More is a classic for me. She is daring. She's written lyrics you wouldn't expect coming out of an MC. She put records out that weren't fashionable for the genre - everyone else was blinging and she came out with the opposite. She's the most important female artist in this country."

"She's fresh and positive and she's got beauty and class," agrees Michael Fountaine, music editor of the black magazine Untold. "She's a breath of fresh air. She's being herself, not styling herself into something else. She's a lovely girl, an around-the-way girl, friendly and accessible. She's sending out a very positive message and there is nothing better than a young black female, or anyone for that matter, sending out a positive message - it's fantastic."

Far from being a nice, easy option for music executives all too aware what a cash-cow black music has become, Dynamite's lyrics are, in their own way, often as shocking as those of Eminem, whom she supported on the UK leg of his tour last year. But while the American star has courted controversy by toying with violence, misogyny and homophobia, Dynamite's agenda is very different. "Tell me who wants to know/ What when who where/ Or how you do your ho?" she sings in It Takes More. "Certainly not me/ Cause baby personally/ I like to be challenged mentally /I've heard it all before /Gangstas pimps and whores/ Quality is poor /A girl like me needs more."

"Ms Dynamite touches on politics and social consciousness like no other. I can't even think of another female artist who does that," says MTV's Jasmine Dotiwala. "People think it's safe because it's not full of swearwords or a gritty female bitch jumping around, but it's hard-hitting. I'd say telling a guy you're not interested in bling bling is political ground. It could shake people up the wrong way - it's groundbreaking."

So how important is she? "If Lauryn Hill was still doing her stuff she'd compare to her, but currently she stands in league of her own. You can't compare her to Mis-Teeq, for example, because while they've got a garage background, their music is very much single girls' party tunes - they're more like Destiny's Child," says Dotiwala.

In Ergatoudis's words, she is simultaneously totally credible and incredible: "The appeal is that she's real, believable, authentic, all those kinds of words. Her honesty shines through; she has integrity. She is able to articulate a lot of things in terms of young, urban street culture, urban life as it affects young people, in a way that a lot of people can't."

But it's not just the lyrics. Dynamite's image also challenges what we expect from our female singers. When was the last time you saw Britney or Beyoncé perform in a tracksuit and trainers? The message to her impressionable female fans is loud and clear: you don't have to expose every inch of flesh to get ahead. "She's not bad-looking girl," says Trevor Nelson, laughing at his own understatement. "But she's not gratuitously sexual - that is a very important part of what she's saying. She's determined not to exploit it [her beauty] too much."

So why the criticism? Surely it must be more than tall-poppy syndrome? "I think it's because she's a girl and she hasn't got her tits out," says Letitia Scobie-Dalrymple, presenter of 1xtra's Weekend Tings. "There's no big blond weave; she looks like a girl who you'd be happy for your daughter to hang out with. We expect a lot of bling bling from female rappers - they want Foxy Brown or Lil' Kim - but that's not what she's about. Her outfits are provocative and appealing, but there's no cleavage, there's no butt. She's saying that kind of thing isn't impressive any more."

To her critics, it's probably bad enough that a black, British working-class woman - and the product of a one-parent family to boot - has risen to the top of her field (in just a year); she can't possibly have done so and maintained her credibility, goes their reasoning. "It's much easier for men to make music that is described as realistic and edgy. When women do it people are more suspicious," says Nelson. You only need look at who she was up against for the Mercury award - David Bowie was one - to see the scale of her achievement. "The nominations this year were bang on point," says Fountaine. "It's not like she won in an easy year. It was a very good group she was in and she won. We must take our hat off to her for that."