Metropolitan Police Commissioner Sir Ian Blair told the Guardian that society must treat children in the families of gang members as if they were at risk.

He told the newspaper: "The solution to the problems of youth violence go far wider than policing. There is a need to think outside the box.

"While the response of the Metropolitan Police and other forces will be extremely robust around youth violence when it is committed, we should also be thinking about how to stop children drifting into these gangs.

"One of the ideas I have asked to be explored is that where an older sibling is clearly involved in gang activity, the right way forward is that there should be a child protection approach for any younger sibling who is clearly at risk of moving into a lifestyle which is extremely dangerous to that child."

Since January there have been seven teenage murders in London related to gang violence.

Sir Ian's comments follow a Scotland Yard report which says there are currently at least 171 street gangs operating in London - although the figure could be much higher.

Some 43% are estimated to have more than 20 members, while 18% have more than 50 members.

Although 90% of gang participants are male, there are believed to be three female gangs operating in the capital and women are often used to "mind weapons" for brothers and partners.