In a rough Glasgow suburb, a mother is celebrating her son's 13th birthday. She hands Robbie a present in a brown-paper. It feels heavy. As Robbie peels the paper off the present, he spots a stout handle and a glistening blade. It's a machete. "We can't protect you, " the mother shrugs. "You have to protect yourself".

This chilling scene in Gavin Knight's Hood Rat sums up the devastating effects of the rising tide of youth gang violence in Britain. The children who kill each other, steal, traffic in and score drugs come from grubby council estates and bleak neighbourhoods. They also point to Britain's growing urban anomie - these young gangsters typically come from broken homes, land up homeless, sleep rough and are socially excluded. Some of them are just plain bored and uneducated, creaming money off benefits to buy drugs and getting sucked into crime.

The young assassins strike in ski-masks and hoods - remember the images from the recent London riots? They are forensic savvy, washing down probable evidence to remove DNA traces and using latex gloves to hide fingerprints. They use mountain bikes, body armour and semi-automatic weapons to "protect" their streets of crowded housing estates. Some of them are as young as eight years old - "by the time you is fifteen you've been stabled up so many times already you're like a veteran", a gangster says.

Knight takes the reader on a scorching roller coaster ride through the blood-slicked, sweaty streets of the "violent, alternative world" which Britain's young gangsters "abandoned by the economy, media, politicians and social infrastructure" have created for themselves. There's plenty of gore and grime in Knight's racy and breathless telling of the story. But it also makes Hood Rat read more like a page-turning crime thriller, rather than a searing, in-depth investigation into the reasons and consequences of youth violence.

Knight loves telling his tale around people, so he digs out some rivetting stories on the hunter and the hunted in the war on Britain's underworld. There is Anders Svensson, a Manchester detective for 23 years who has investigated 30 murders and is on a mission to take out two gangsters from the streets. After he finally puts Merlin and Flow behind bars after a lifetime of work, Svensson returns to an empty home, his second wife having left him with children.

In London, a teenage êmigrê from violent Jamaica goes by the name of Pilgrim and rules the street. In another nail-biting sequence, he plunges into a manhole even as police helicopters hover over him and escapes through the sewer. All this until Troy, a 14-yearold boy from Mogadishu who cut his teeth in killing with warlords back home, begins to rule the streets. Troll, by the way, has been robbing people since he was eight and became an active gang member at 12. And in Glasgow, the most violent city in Europe, policewoman Karyn McCluskey - who seems to be remarkably like Marge Olmstead Gunderson, the likeable and bright police detective in Coen Brothers' Fargo - is on a mission to end gang warfare by talking to the gangs themselves.

In London, Knight trawls the seedy underbelly of Southall, obscured by the bustling, thriving ghetto of Sikhs. Southall is the cheapest place in Britain to buy top quality drugs - a Sikh junkie says a friend died because the heroin in Southall is "too strong" - and where Sikh and Somali gangs trade in drugs, fight and steal whatever they can. Where groups from Ludhiana sleep rough in derelict pubs and crumbling estates. It is a welloiled business: the Somalis and Sikh junkies steal for their fix, and the Afghan-Sikh hawkers buy their booty. There is a moving sketch of a Sikh junkie-thief called Jas, son of a Punjab farmer and who arrived with a student visa to study business management at a London college. He quickly used up his father's money on rent and landed up homeless and high on heroin on the streets of Southall. Jas and his fellow junkies meet at the famous gurudwara, where framed by a huge portrait of "one of the Sikh saints, Sant Jarnail Bindawarra" (a rare instance where Knight gets it awfully wrong) talk about the invasion of the Golden Temple, "Indian oppression" and an insensitive media back home. Moments later, they are scoping the streets for heroin.

In Knght's vivid and adrenaline-shot prose, Britain's underworld is an abandoned, desolate dystopia steeped in gun crime, gangs and drugs. It is peopled by children who fight with hatchets, poles, samurai swords, machetes, knives, clubs, bricks, bottles and whatever else. What Hood Rat direly lacks by way of deeper context, it makes up with giddy drama.