Once, teenagers used to gather, smoke a little weed and debate the merits of gangsta rappers on the steps outside Frenchies barber shop.

The dilapidated corner of Spital Hill, in the heart of Pitsmoor, a rundown part of Sheffield, was regarded as a haven from a gang turf war where members of S3 Army and their rivals S4 could mix. It is no longer.

Now it marks the front line of one of Britain's most vicious, and inexplicable, street feuds between gangs who name themselves after two of the city's postcode districts.

Each night since 17-year-old Tarek Chaiboub was shot dead outside the shop by an even younger gunman, it has been haunted by mourners, led by his girlfriend Bianca, elegant as a catwalk model, and a small army of youths. Several wear the street uniform of pulled-down hoody, chunky Nike trainers and webbed gloves.

Chaiboub, known as GT for Global Threat, was a gifted, popular and generous teenager with an easy way of making friends among a group whose style of rap music translated their common experience into a poetic but incessant street patois. He was shot on the street pitch where he is also said to have dealt crack cocaine.

His death, ten months after that of his friend Jonathan Matondo, 16, another rapper, amid an escalation of gang violence, has suggested that Sheffield is nurturing a gang culture every bit as virulent as that of Britain's largest cities. The sudden death of such a well-known figure has shocked even hardened gang members.

One pale-faced youth, looking on as Bianca lit yet another candle in a scene of theatrical yet powerful grief, said: “All this repping sh** is stupid because too many innocent boys are getting killed.”

Along with gangsta rap and street uniforms, the concept of “rep” is central to gang culture: the nurturing and protection of a reputation, reinforced by a street name, which members go to extreme lengths to defend.

Many disputes begin with a real or perceived breach of street etiquette that slights a gangster's reputation. Members are expected to guard their “reps”, meaning that the most minor of incidents can escalate into violent feuds.

Members of S3 Army, who favour black bandanas, have been engaged in a feud with their rivals, the S4 in green, for so long that few can now truly recall its origins in a simple falling-out among families. The arrival of guns and a lucrative trade in crack in recent years has led to an escalation in the stabbings and shootings and has drawn in, and polarised, large numbers of black, white and Asian youths.

The S3 and S4 rivals, who model themselves on Los Angeles street gangs, are divided by geography rather than ethnic ties: both comprise black, white and Asian youths. They compete for turf in the Burngreave area of the city.

They favour Russian-made Baikals - self-loading pistols converted to fire bullets rather than gas canisters. Each gang has its own rappers and their social networking site of choice is Bebo.

Burngreave is multicultural, with poor white families living alongside blacks, Asians and significant populations of Kurds, Somalis and Yemenis. Along Spital Road, West Indian food stores vie with Kurdistan restaurants, money transfer shops and ethnic cafés. A knot of young black men mill around outside the Kashmir Curry Cabin and a derelict garage lends an air of hopelessness.

The youths on the streets, their heads encased in ubiquitous hoodies, their upper lips covered with a wispy fuzz, are sullen; they burn with an inarticulate sense of grievance bordering, in some cases, on paranoia. They speak haltingly about the pressure imposed by their own kind of postcode lottery.

None of those wearing tight-fitting gloves on a warm summer's evening admitted to being a gang member but each appeared acutely aware of geographical loyalties. One youth offered a vivid insight into Sheffield's gang culture.

“Pitsmoor is both S3 and S4. We all used to go out as one big family, hanging around with each other. After one thing or another happened, it all split up and certain people just didn't like certain other people,” he said.

Despite tarnishing the area's reputation, he insisted that the streets were safe for outsiders to walk. “People look at Pitsmoor and say, ‘I'm not going there, I'll get shot or stabbed.' But it is not like that. No random person is going to get stopped on the street or nothing like that.”

Another youth, who called himself Danny D, said: “I live in S3 but I don't wear no bandanas. I have finished college and want to get a job. I don't want to end up on this street corner.”

The candles and floral tributes for Chaiboub, described in gang patois as an “S3 soljah”, spread along the gutter where there were still traces of the sand used to soak up his blood. One black teenager in a baggy Nike T-shirt said: “He was a good guy who would give up his last few coins to make sure you didn't go hungry. He used the lyrics of his songs to talk about how it really is on the streets.

“He always had so much life in him. You only had to chill with him for five minutes to feel nice. That's how I remember him.”

Chaiboub once boasted in one of his raps that: “I cause more chaos than World War Two,” but he was brought up within a close, loving family in Wincobank, S9, several miles from Pitsmoor, and took up a short-lived apprenticeship in building after leaving Myers Grove school. Despite growing up across the city, he was drawn to the street culture of S3.

His father Rashid, 44, a Syrian restaurant chef, called him his “self-confident shining boy” but confesses that he lost his son to knives and guns some months ago. GT became the Terror Kid.

The streets of Pitsmoor have been volatile since Jonathan Matondo, a 16-year-old Congolese, was shot dead last October in a recreation ground less than half a mile from the spot where Chaiboub fell. His death followed a shoot-out near by between the S3 and S4 gangs. Matondo, nicknamed Venomous, was a friend of Chaiboub, who later wrote a tribute rap called RIP VenDogg.

Events then moved with brutal speed. Earlier this month, Brett Blake, a car dealer aged 23, was stabbed to death on the dancefloor of the Uniq nightclub in Sheffield. Ominously, a website tribute carried the message: “Justice will be done.”

Five days before his death Chaiboub was “webbed”, stabbed seven times in the legs and lower body, in an ambush outside his home. The knife narrowly missed organs but the attack was not enough to stop Chaiboub, now armed with a gun, limping back to the front line on Spital Hill on Friday lunchtime where he was ambushed and killed.

A recent paper by Manchester University academics suggested that British gangs are messily chaotic around the edges. In Pitsmoor, gang membership appears amorphous.

One police officer said: “It changes every day depending on who you are talking about.”

Much public money has been invested in the area, at least £52million under the Government's New Deal for Communities scheme. Spital is dominated by a new office block now awaiting its first small business tenants. Youth workers are an energetic presence, the latest initiative a conference, Teens in the Hood, organised by the youth team Streetworx.

However, one community leader, who asked not to be named, said: “If a young man gets £100 a day for dealing in drugs and is then arrested and jailed for 18 months, there will still be ten more queueing up ready to work for such rewards. Why work for £80 a week?”

Jackie Drayton, a Labour councillor in the area, used to console herself that there have been gangs in the city ever since the 1920s and, anyway, the violence is targeted not random. These thoughts are becoming less reassuring.

“I am thinking now that if I were a young person might I be just a little scared?” she said. “If I was walking down the street, and people did not know who I was, maybe they might mistake me for somebody else.”

Chaiboub always knew the risks of setting himself up as a “true Sheff soljah”. He went as far as predicting his own death in one of his raps, singing: “If you don't watch out the last thing you'll hear is click, click, pow.”

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