More than a third of all murders in London are the work of criminal networks, new police research shows.

Of the 170 known gangs in the capital, over half are involved in serious violence. Two thirds deal in more than one illegal trade besides drugs.

These findings, part of a study commissioned by Met chiefs, will be used to fight organised crime more effectively.

Blackmailing their own kind

Almost half of the mapped networks are based on shared cultures, including 24 nationalities. Of these, police will prioritise:

  • Turkish and Chinese gangs involved in people smuggling and blackmail of their own communities.
  • Vietnamese groups with large-scale cannabis plants.
  • Columbian cocaine networks.

Other gangs are based on geographical proximity (42%), family (9%) or Internet rings for paedophiles and money laundering (2%).

Almost half of the mapped networks have international links.

Researcher Anna Aquilina said not all of the gangs are highly sophisticated. "A lot of the networks posing the highest harm and threat to communities are chaotic and disorganised."

New focus

Where police previously targeted single crime types, such as drug trafficking, they will now focus on the individuals and networks behind a host of offences.

They will aim to take out key people, such as an expert money launderer who filters the proceeds of an entire group.

Officers will also remove lower members, forcing those higher up to become more "hands on" and easier to arrest.

In the last year the Met disrupted more than 50 gangs and it plans to double that figure in 2006/07.

Gun factories

The announcement came hours after eight people were arrested in a police raid of a cannabis factory in a terraced house in Woolwich, south-east London. More than 800 plants were found in six rooms in Woodhill at dawn yesterday.

Other recent breakthroughs include the conviction of a Columbian gang that smuggled at least £38 million of cocaine into Britain. A total of 48 people - 34 in the UK and 14 in Columbia - were sentenced to nearly 400 years in prison.

Last year police arrested the head of a £4 million British network based in south-east London. Andrew Pike, who had home in Croydon and Rochester, Kent, has been convicted of conspiracy to supply cocaine after being caught with 500g of the drug in his car.

Intelligence showed he was the brain behind two firearms factories, in Plumstead and South Norwood, where blank firing guns were turned into lethal weapons. The guns and ammunition were used in several drug-related murders and one attempted murder.

"The shape of crime is always changing and we are shifting our approach to meet these new challenges," said Assistant Commissioner Tarique Ghaffur, who commissioned the study.

"What we are seeing is not a worsening situation, but rather the Met taking an intelligent approach to putting our resources into those networks that are causing the most harm."