London's crack wars
At first police believed they were a loose association of criminals bent on little more than making money from drugs and spending it as quickly as possible.
But a spate of recent killings has worried police in London that the capital faces a new threat from organised gangs known as Yardies, who frequently resort to guns to ensure their status in the illegal drug trade.
Last week saw the latest murder in a brutal turf war between rival groups, mostly made up of Jamaican migrants fighting for control of the crack cocaine trade in Britain's inner cities.
Dean Roberts, a 20-year-old minor drug dealer, was shot dead in a street in north-west London by two men armed with automatic handguns. It was the 13th such killing in the area to be linked to the Yardie gangsters this year.
The gunmen made little attempt to hide their identities and police believe the same gangs have been responsible for other shootings, including one in May when a young couple were shot dead at home in front of their seven-year-old daughter.
The extent of the feud was reflected in another incident last week at a shoot-out between rival factions outside a north London nightclub.