They are Yardies and in terms of a reputation for ruthless violence they could one day rival the Triads or Mafia.

A spate of violent killings in London's black community has raised fears that the capital is witnessing a renewed bout of Yardie gang warfare.

It would not be the first time. Almost 12 months ago similar predictions were being made after three murders appeared to be linked to gang activity.

A Yardie in Kingston, Jamaica, shows off his gun

That it failed to materialise was seized on by those who feel the Yardie phenomenon is more myth than reality.

Certainly the Metropolitan Police do not formally acknowledge the existence of Yardie gangs. They refuse to use the term publicly, although the Met's Operation Trident is widely seen as an effort to combat Yardie crime.

Trident, which started life in south London, has been compiling information on the crossover of gun and drug culture and investigating shootings in the area. It is currently being rolled-out across the capital.

Yardies is the term applied to Jamaican-born gangsters operating in Britain. The name refers to criminals from the impoverished back yards of Kingston, Jamaica.

Copy-cat criminals

Recently, their traits have begun to be mimicked by small numbers of British-born black youths drawn to the "glamorous" gun-toting image.

One reason for the police's reluctance to pigeonhole Yardies in the manner of other organised crime groups could be their lack of organisation.

There is no central control or brotherhood structure, so Yardies have few affiliations or loyalties. Gangs are very loose knit and often fall out with each other.

Smoking crack: The drug's rise is mirrored by that of Yardies

Members are mostly linked to drug and arms dealing as well as robbery. It is a lifestyle synonymous with violence - impulse shootings and gangland-style executions are used to sort out internal squabbles.

The Yardie phenomenon in the UK was first noted in the late 1980s and their rise is linked to that of crack-cocaine, in which many trade.

Since then their reputation for ruthless violence has grown with each shooting. In 1993 Yardies were blamed for the cold-blooded murder of PC Patrick Dunne, who was on patrol in Clapham when he stumbled across a shooting incident.

The gangsters hit the headlines again in 1997 when police tactics to infiltrate the underworld were exposed in a World in Action documentary.

Metropolitan Police overlooked a series of violent crimes carried out by two Yardie informers, Eaton Green and Delroy Denton, while they passed on intelligence to Scotland Yard. While an informer, Green was involved in the UK's largest armed robbery, when 150 people were held up at a blues party in Nottingham.

In the past six weeks alone, Yardie involvement has been suggested in five black-on-black murders in London.

In one double murder last month, Laverne Forbes, 28, and her partner Patrick Smith, 31, were shot in the head in their north London flat. Their seven-year-old daughter witnessed both killings.

Laverne Forbes: Murdered in front of her daughter

On Monday a 51-year-old sound engineer, Henry Lawes, was gunned down by a gang of five men outside his home in Harlesden, north west London. His killers waited until he fell over before ruthlessly finishing him off.

Detective Superintendent Peter Camiletti, who set up Operation Trident, suggests the recent tide of murders may have been sparked by an infringement of the unwritten code of conduct.

"There seems to be in this culture, a culture of respect for each other's status. If disrespectful acts take place that can lead to revenge attacks," he says.

Their expensive tastes can make Yardies highly conspicuous. Wealth is something they flaunt, often in the form of flashy cars, gold jewellery and designer clothes. Moschino is a favourite label.

Nightclub murder

Image is everything in their world, as the notorious death of Mark Burnett demonstrates. In 1991, Mr Burnett was shot dead in the middle of a London nightclub after he accidentally stepped on the toe of a Yardie gunman.

Yet stories like this have only bolstered the Yardie image of merciless brutality and, according to some, helped perpetuated what is little more than a myth.

Journalist Tony Thompson, who researched the Yardie underworld thoroughly for his 1995 book Gangland Britain, concluded that while Yardies definitely exist, their influence has been blown out of proportion.

Across the UK, he estimated Yardies numbered between 80 and 200 in total. Yet between 1986 and 1995 he estimated they had been responsible for 57 murders.

Life is short

Retired Detective Superintendent John Jones, who investigated the Yardie scene in the early 1990s, has said killings are worn as a "badge of honour" and tell others "they are not to be messed with".

But the cycle of violence is such that a Yardie never stays on top very long. Their live-for-the moment philosophy explains why, according to Mr Jones, the average life expectancy for a Yardie is 35.

Despite their lack of discipline, the "here today, gone tomorrow" culture is a major obstacle to police efforts to infiltrate the fraternity. Added to this is the climate of fear that pervades any culture of organised crime.