Calling it "gang culture" doesn't help, yet territorial rivalries among some young Londoners are spreading, escalating and blighting entire neighbourhoods

Page 81 of my London A-Z shows the streets, parks and stations at the intersections of north Westminster, north Kensington and Brent. But it offers no clues to the alternative cartography that shapes the lives of many people living there ? an unofficial map of an urban landscape scarred by violence and divided by fear.

The page's top edge shows the elegant Queen's Park, in whose surrounding streets live barristers and media dignitaries in homes worth a million pounds. Further down, the eye falls on Maida Vale and Notting Hill, synonymous with wealthy, wedding cake terraces.

But for the past two or three years the space in between ? the A-Z calls it West Kilburn and its fringes - has seen a succession of shootings and other violent attacks arising from feuds between youths living in and around two estates that stand just a ten-minute walk apart. These two estates ? the Mozart, which lies in Westminster and the South Kilburn in Brent - are the focus of rivalries acted out in accordance of a different street map entirely.

Territories have been defined and the borders between them guarded and sometimes breached. Incursions resulting in chasings, beatings and robberies are frequent. Intermittently, the more serious incidents are declared news. A recent example occurred in September after three young women, all teenagers, who were gathered outside as part of a larger group on the Mozart, sustained shotgun pellet wounds from an attack by an unidentified male youth who fled the scene on a bicycle. One of the teenagers was holding an 11 month-old baby

Three months later a man in his early twenties survived being shot twice in the chest on the Mozart. Last month, another young man was shot in the back near St Augustine's school on the Westminster-Brent border, an attack believed by well-placed authorities in the area to have involved boys from the South Kilburn estate and its orbit. The victim of this last attack has appeared prominently in videos made by a local rapper. Music clips posted on YouTube or Spiff TV are part of the armoury of wind up, insult and beef.

Some who live in the area concerned, including some who are young, are barely touched by this wired, short-fused youthful world. They and it are largely invisible to each other: people move freely and routinely to and from work, local schools, community facilities and places of worship just like anywhere else. Yet an awareness of that other side of neighbourhood life has filtered down even to primary school children. And on the streets young people in particular, even if they have little or no direct connection with it, are acutely conscious of it: at worst, cowed, menaced and controlled.

I visited a family whose teenage boys are now never, ever, let out alone. One has been shot by an unknown assailant. Another endures repeated threats from youths on the other side of an unofficial boundary part of which runs through the junction of Carlton Vale and Kilburn Park Road. A recent, supervised excursion to the adjacent Paddington Rec was marred by a group of adolescents from enemy territory gathered nearby. Challenged by adults, they said they were "patrolling."

The family affected is desperate to move, preferably out of London altogether. They are dreaming of Slough: John Betjeman is turning in his grave. For others, the threat is far less acute, yet still too real for comfort, even if only in the mind. Stand-offs, displays of strength and occasional raids behind enemy lines are described as commonplace. Lately, some have been hiring minicabs in order to make incursions behind enemy lines, hurling drive-by taunts, threatening with weapons and reportedly even assaulting youths at random.

Why the escalation? Why the hardening of dividing lines and attitudes? Some date it from the murder in May 2010 of 22-year-old electrician Daniel Smith on Harrow Road in what police said at the time they believed was a case of mistaken identity: three men in their twenties were later charged with murder and are expected to stand trial soon. The following October came a report that a 13-year-old was kidnapped for 24 hours by a Mozart estate gang, pistol-whipped and released only after a ransom was paid. The local West End Extra was given to understand that the child refused to co-operate with the police.

Yet telling this story as a series of brutal incidents risks missing the bigger picture. According to some of those trying to deal with the situation ? youth and community workers, schoolteachers, local police - even those playing this deadly game can't put their finger on specific reasons for the hatreds or any clear pattern of cause and effect. All that's plain is a self-perpetuating cycle of slights, assaults and retaliations that range from the minor to the grievous.

Is this world captured by that recent addition to politicians' vocabulary, "gang-culture"? It's not that simple. There is overlap between the street kids and serious, older criminals, which involves some in drug-dealing, weapon-handling and robbery. But at the adolescent end of the spectrum the psychology at work appears to be still rooted in the end of childhoods ? childhoods variously marked by family troubles, financial hardship, emotional trauma and a simple, perhaps desperate need to belong.

Few who strive to deal with it close up doubt that it's a psychology that is proliferating in London life, embedding itself more deeply in more and more of the city's social landscape. There are other unmarked boundaries on my A-Z's page 81, including the Paddington branch of the Grand Union Canal, whose curving course just to the south of Harrow Road divides lower West Kilburn from the environs of the top end of Ladbroke Grove in Royal Kensington and Chelsea: one confrontation near this aquatic line of demarcation led to kids throwing themselves into the water to make a terrified escape.

In this increasingly less subterranean world the streets are an excitingly dangerous playground ? a place that's more available, more plausible and more rewarding than the alternatives of education, conformity and long-term, steadier rewards. Yet though that playground may be larger than those at primary school, it is both limited and limiting too. The horizons of those playing crazy, deadly games there don't extend geographically, intellectually or emotionally even as far as A-Z pages 80 or 82. Changing that may be part of the solution. It's a subject I'll address tomorrow.

Names, identities and locations have been omitted or obscured in this article in order to avoid adding to local tensions or undermining the efforts of those striving to lower them. I am extremely grateful to everyone who gave me their time and thei
r feedback on draft versions of this article.

Update, 2 March 2012. My promised piece on finding solutions to this problem has now been launched.