Brenton Brown, By Alex Wheatle

From time to time, a new book arrives which catches its moment in an almost uncanny grip. Set in the middle of the last decade, the latest novel by South London writer Alex Wheatle has an all-too-obvious connection to this week's blazing headlines. At one point, a grieving teenager voices her scorn and fury at the mayhem unleashed by a junior gangster who has shot her boyfriend in error after a nightclub assassination struck the wrong target: "he's probably boasting to his crew right now... He's probably writing about it on his fucking MySpace page... What is wrong with these idiots? Don't they have parents who bring them up right? I bet he's got a pic of him on his site doing some bullshit macho pose. His bredrens are probably saying, yeah, you're a soldier. A fucking soldier! Is that all they live for? To be called a soldier by their wasteman crew?"

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That MySpace – rather than Facebook – allusion fixes the date. Brenton Brown, a sequel to Wheatle's much-admired debut Brixton Rock (1999), often slips back into a tormented past. But its main action unrolls from 2002 to 2005, through a period of comparative hope and calm.

Brixton Rock – with its echoes of Graham Greene in title, plot and mood - introduced the perennially out-of-place Brenton. Brought up in a rural children's home, a volatile outsider in Brixton, he grew into a young man ill-at-ease, in every way, in his own soul and his own skin. It also portrayed his sulphurous affair with half-sister Juliet, a dangerous liaison that tugs Brenton back into a swamp of bad memories where rage and self-pity mingle. Always alert to the tangled roots of despair and disorder, and never a one-note chronicler of "ethnic" London, Wheatle in his fiction echoes the question that Brenton's Oxford-educated social worker asks during the hero's youth in care: "Why it's so difficult for the working-class to progress".

Now, at the zenith of the new Labour era, Brenton holds down a job as a decorator in the gentrifying streets of a neighbourhood that no longer quite counts as (in the title of Wheatle's previous novel) The Dirty South. In designer bars, he gazes with a jaundiced eye at the WMCBs ("wannabe middle-class blacks") as their sip their cocktails: "at least they're trying to move up from having lunch at Kentucky". Juliet, meanwhile, has soared: a high-flying Lambeth Labour councillor, with ambitions to enter Parliament, she has married a suave (black) investment banker, Clayton. She lives with him and teenage Breanna: her daughter, but not his. In what now feels an especially poignant scene, Clayton – who claims his heart "is still in this community" - donates £50,000 of boom-time bankers' cash to a thriving youth club.

Yet shadows darken these Noughties vistas of upward mobility. Gang crime robs Breanna of ambitious and responsible Malakai, who "didn't want to be part of some fucked-up crew that traded in showing how bad they were". And the trashy allure of the "bad breed boys" still pulls some of a younger Brixton generation down.

Ever since London first sprawled into a metropolis with an insecure, disposable proletariat, it has hosted authors who investigate the city's lower depths and report on what they find. As far back as the 1590s, Elizabethan pamphleteers evoked the rogues and vagbagonds of filthy alleyways with the flesh-creeping relish of literary tourists among the underclass. This mean-street titillation continued through the vice-ridden Georgian lanes of Defoe and his peers. It reached its apogee in the numerous sub-Dickensian accounts of reeking slums and low-life villainy with which Victorian gentlemen of letters regaled a deliciously appalled readership. Images of a dangerous, criminalised rabble shocked and thrilled the bourgeois voyeur.

Later in the 19th century, those accursed residents of slumland slowly won the chance to speak for themselves. Pioneering researchers such as Henry Mayhew, in his London Labour and the London Poor (1861-62), tempered moralising with heroically detailed reportage. The capital became, as it remains, an "arrival city", crammed with new communities: first from rural England, then Wales and Ireland, then continental Europe, then the former Empire, then the whole world.

In time, the incomers found a literature of their own. Read Israel Zangwill's Children of the Ghetto (1892), set amid the Jewish community of Whitechapel, and you glimpse in prototype just that blend of genuinely well-informed testimony and often comical melodrama that brands a hundred later exercises in inner-city London writing. Insiders, brought up among the people they describe, could like the visitor-voyeurs fall into the traps of sensation or sentimentality – often conveyed through "authentic" slang.

Even a classic such as Sam Selvon's pioneering The Lonely Londoners (1956), about the Windrush generation of Caribbean migrants, does not entirely shake off this strain of folkloric anthropology. The pull of the genre has proved hard to resist. For all its generous intentions, a contemporary example such as Stephen Kelman's Man Booker-longlisted novel Pigeon English rather goes overboard with its fabricated sink-estate patois.

With its spasms of violence, meticulous period soundtrack, niftily-crafted "street" dialogue and expertly-dressed social types, Wheatle's Brixton fiction can't quite avoid the hallowed conventions of the urban shocker. He does not try to gratify sensation-seekers, however, and has for years run literature workshops with just the kind of hard-pressed inner-citizens who populate his books. What distinguishes Brenton Brown, as with Brixton Rock, is a rich layering of motive and emotion that lifts his protagonist far above the pundits' platitudes.

Above all, in Brenton's still-enraged mind, social and psychological obstacles to his contentment fuse. So he – and we - can hardly see the joins. That complex motivation makes Wheatle a true novelist, not a sociologist – along, of course, with the robust dialogue, streetwise humour and muscular, mischievous vernacular that grace this book. Brenton has learned to talk the Brixton talk, but did he walk the walk? Not according to old friend Floyd, who recalls "some kinda BBC, Surrey fuckery going on" with the care-home survivor's accent, and above all his rustic waddle: "That was some farmer, cow-nibbling, sore-bunion, straw-yamming country-bumpkin kinda walk, dread." For this you forgive, or accept, the late lurches into melodrama and the broad-brush cartoon satire of Juliet's creepy political habitat.

In his 2001 novel East of Acre Lane, Wheatle – a witness to those events – dramatised the Brixton riots of 1981. With its backdrop of fragile aspirations, and of a needling tension between a new black middle class and the brazen "soldiers" of the street, Brenton Brown does not directly address the destruction and self-destruction we saw again, in a more tragic key, this week.

Yet, via the mixed feelings and scrambled identity of its hero (who even in his hard-working artisan's life can seem to younger tearaways like "a proper Brixton badman"), it does perform fiction's proper role. It makes us see that strife – on the streets or in the mind – may have many fathers. Both actors and victims, free to change but pressured to repeat the patterns of the past, Brenton and his fellow-Brixtonians show that acts (however reckless) have multiple causes. But they also have "consequences" – of guilt, of hurt, of harm – that will "last a lifetime".