For any English scribe, the prospect of spending several seasons in the urban jungle of South Central LA is a pretty intimidating one; not so much Orpheus descending into the Underworld to redeem his love as a hack hits the backstreets in search of some hot copy.

The writer in question, William Shaw, is no hack, but his third book Westsiders is indeed a hot piece of reportage. This isn't the first time the writer, a contributing editor of Arena, has gone undercover - he had previously penned a mole's eye view of English religious nuts in Spying In Guru Land, but this time out the stakes are much higher.

In profiling a bunch of unrecognised young rappers feverishly trying to claw their way out of the ghetto, Shaw tells not just their stories but the stories of the street: Watts, Inglewood, Southgate, Compton - a hip-hop hotbed boxed in by the Harbor, Long Beach and Gardena Freeways, endless criss-cross networks of dirty boulevards peopled by young men with shaved heads in plaid shirts leaning against trees or sitting on doorsteps, watching cars cruise slowly by prospecting for weed.

Characters like Babyboy, Khop, C-Double-E, Tibu and Kokane live under the ever-present shadow of being killed in a random driveby shooting, or by gangs of armed 12-year-olds roaming the city at night. To get by, they deal drugs, dream up scams, record demos in small shack-studios or form entertainment companies that exist only in their heads and on the business cards they distribute at hip-hop conventions and club shows. Others scrape a living as street promoters, acting as freelance pluggers for the major labels, plastering lampposts with flyers, ringing up radio request lines, pestering retailers and DJs, handing out merchandise at shows, passing around clip tapes at schools. Here, everyone is trying to find a way of "clocking them ends": making money, or if you prefer, "Benjamins", "dead presidents", "cheddar", "scrilla", "scratch", "chips" and "gravy". Here, Wu Tang's CREAM rule applies - Cash Rules Everything Around Me.

So, Shaw's book is not just the tale of a locale but a language: hip-hop as a post-colonial prison culture, reflected in the street styles of baggy assed jeans with no belts and sneakers with no laces, as well as the ever mutating strains of encoded slang. And if South Central sounds like another planet, imagine how a white Brit like Shaw felt while moonlighting in the 'hood.

"I kind of feel that if you're going to persuade people what you've done is worth reading, you have to do something that they can't do," the author reasons. "They're buying your vicarious experience, so you've got to take them to a place that they're not going to go (by themselves). There's a rash of journalism at the moment talking about the everyday, and I'm incredibly jealous about some of those journalists, they get to write about staying at home bringing up their kids or whatever, but I just don't feel that I could do that."

On another level, Shaw is also engaged in is the dismantling of archetypes, trying to take the mask off the black bogeyman who has scared the crap out of the white middle class ever since the emergence of Robert Johnson, never mind NWA.

"It's almost that, things that you find spooky as a kid, if you go to them, they might still be spooky, but you understand them," he reckons. "If you immerse yourself and you learn the language of it, it's sort of transformed into something else."

So was he scared?

"I was pathetic at the beginning," he laughs. "I was really scared, and I think you realise that it's a really scary place. A lot of Angelinos don't go there. I was very, very aware of the omnipresent threat. But I'd been hanging around with a lot of these kids, and the threat's to them, not to me, and that took me a long time to realise. Towards the end I was going to Compton quite a lot, and that is a scary place, there has been a lot of random violence there. But you learn the rules that everybody does in those places: you don't go anywhere after dark if you don't know where you're going."

In fact, Shaw reckons his Englishness actually worked in his favour, guaranteeing him a certain amount of immunity from parochial gang hostilities.

"It's the only time it has!" he says. "Weirdly enough, in the summer I went back and met up with Babyboy, who's finally recorded an album, and he wanted my voice for it because it's such a gimmick, 'Hey, there's a guy there with a stupid voice!' Which I can take!"

Did he find it hard to watch all these kids struggling?

"Yeah, it was," he says, "because you knew that they didn't stand a chance, generally. It's different for them, because most of us have ambitions or want to be in bands and things like that, but as you went on, you realised it was a lot more than that. Like that guy Rasheed Rah, he was desperate to be on the map for reasons that were really important to him. I keep using the expression 'putting yourself on the map' but it seems incredibly appropriate - that sort of thing about letting your geography be known. You give names to your street, you give names to your friends and you tell about yourself."

As Shaw indicates, the hunger for fame is a far fiercer urge in South Central than in mainstream America and Europe, where it's still predominantly a middle class, vaguely bohemian aspiration. Over there, the rap game is a matter of naked survival, the only viable alternative to prison, the pipe or the funeral parlour

"The thing that comes over again and again is they're sick of hearing about friends who died and nobody cares," Shaw points out. "Therefore it's not just fame for yourself, it's fame for your neighbourhood. Nobody in Britain would know about Compton had it not been for Eazy-E, and Compton's quite a big place! I think that's incredibly important for the people there. Even if it's given it an even shittier reputation than it had, there's a level on which they feel they've really achieved something, and I think you've got to say they have."

There's another theme running right through Westsiders - that of the strange relationship between the black ghettos and the white suburbs. The whiggers crave the street cred of the ghetto boys, who in turn desperately want to live in those mansions on the hill.

"I still can't figure out what it says about a society where the dominant culture is one that reveres its own underclass and yet at the same time holds it at arms length and ensures that it is an underclass," Shaw considers. "White boys - especially at the phase when gangsta rap happened - really wanted to hear how bad people were, that if you came into contact with them, evil would happen. Ice T, who's by far my least favourite musician, I can remember right at the beginning when he was doing things like Home Invasion, he figured out that this was about adolescent white boys' fantasies about their parents' house being broken into by black people. And that was a stroke of genius in understanding that sort of weird mentality.

"But I think that's what happens when you get a society that becomes completely hidden from itself. Two sections of America don't see each other: you think, 'People ten miles away don't know about this'. It's such a class-ridden society that believes it's completely classless."

One of the more fascinating episodes in Westsiders concerns an Inglewood MC contest in which one of the newcomers is one of those geeky white kids, a young cut-up by the name of Eminem. Marshall Mathers lost out in the final round of the competition, but it was to prove a vital juncture in his career, as Dr. Dre's Aftermath emissaries were impressed enough by his performance and demo tape to offer him a deal soon afterwards. Did Shaw recognise the significance of the event at the time?

"I have to be fair, I didn't," he admits. "If you looked at the first draft just before I handed it in, just about when Eminem was coming up, I had written it entirely from the perspective of the audience, thinking it was fascinating seeing their reaction to him 'cos I just thought there was a level of honesty there which I wasn't expecting.

"I thought one of the tragic things about South Central in some ways is that I received very little racism, and he received no racism that night apart from one performer, and the audience hated hearing that racism in a way that I don't think our own society would live up to, so that was quite impressive. They weren't treating him as a novelty; they were treating him by the fact that he was obviously quite an extraordinary talent at that point.

"I took lots of notes about it, but it was only in retrospect that I sort of put that scene together, because it was obviously so important. I'd written in my notes 'M+M', and when the first Eminem stuff came out I didn't connect, it took me a couple of minutes and I thought, 'God, that was that guy I saw down at The Proud Bird'."

Apart from Eminem, Shaw managed to bag interviews with an impressive amount of West Coast playas, not just the likes of Tupac and Ice Cube, but Rodney King, whose savage beating at the hands of the LAPD sparked the LA riots in 1992. Shaw met the latter when he was launching his own label Straight Alta-Pazz at a niterie on Hollywood and La Brea.

"People like Rodney King, when I heard his label was coming out I thought, 'I've gotta get him'," he explains. "I am a working journalist and you suddenly realise you're allowed to call people up. In lots of ways, I much prefer writing about people who aren't famous than are. But I quite like the idea of those parallel lines of people who've made it on one end and those who haven't on the other, and if you put them together, somehow the two types of story reflect back on each other.

"One of the things that actually sparked the whole book off was I'd been interviewing people like Tupac," he concludes, "and you see them talking about their youth all the time and it's incredibly powerful stuff, and you think, 'These people lived a life apart from us'. That's what made me want to do it in the first place: 'What's it like if you go back to find an 18-year-old Tupac?'"

Only time will tell if Shaw actually discovered such a candidate, but as he says, the underdogs are even more interesting. Either way, Westsiders is a pretty powerful piece of modern LA noir, worthy of being filed between Mike Davis' City Of Quartz, Joan Didion's White Album and Ronin Ro's Have Gun Will Travel. Check it out.

Westsiders is published by Bloomsbury and retails at £11.99.