London's growing gang culture needs to be tackled before there are more murders like the shooting of James Andre Smartt-Ford at Streatham Ice Rink, Met Police commissioner Sir Ian Blair says.

Speaking at the monthly meeting of the Metropolitan Police Authority, Sir Ian called London's gang threat a "cloud on the horizon".

Scotland Yard have identified 169 gangs with about 5,000 members in London.

Sir Ian said there was a danger of adding to the "allure" of gang culture by overstating its importance.

"It is a cloud towards the horizon that is coming," Sir Ian told the meeting.

"Unless we do something about it, it will get very difficult."

Sir Ian said most gang violence victims knew their attackers but refused to identify them to police for fear of reprisals.

"What we have to find is a way of encouraging these young people to trust the authorities to protect them," Sir Ian said.