London's new crime "sheriff" said today the capital was at risk of a gang problem on the scale of Los Angeles unless police took action.
Kit Malthouse, head of the Mayor's Office for Policing and Crime, said gangs were allowed to take root over the last 10 to 15 years and it could take another decade to eradicate them.
Speaking at the launch of Scotland Yard's new gangs task force, he said he first called for a similar specialist unit in 2008 soon after Boris Johnson was elected. He told the Standard: "I don't know why the Met did not agree. I don't think they understood the scale of the problem."
At the time, youth crime was soaring and the year saw a record number of teenagers murdered in London.
Mr Malthouse, in charge of setting Met strategy and budgets, said: "These gangs were allowed to seed and fester in the last 10 to 15 years and this now presents us with a problem that will take a sustained effort over a number of years to eradicate.
"If we don't deal with this now then in the next five to 10 years we might end up like Los Angeles, where gang culture has taken such a hold that they have to learn to live with it.
"We cannot let London go that way. There are already alarming signs of it. God knows what Ken Livingstone and Tony Blair were doing but somehow gangs were allowed to grow.
"We welcome the launch of the gangs unit. This is a significant development. Met Commissioner Bernard Hogan-Howe has had considerable success against gangs in Liverpool and we hope for the same here."
Mr Malthouse said some boroughs had already achieved success in tackling gangs - notably Hackney, which has seen significant falls in violent crime and gun offences. The deputy mayor added: "The only alternative to tackling gangs is to ignore them - and ignoring them leads to mayhem and death.
"I use this analogy. If the city was
full of groups of individuals organised into areas where they were abusing toddlers then the Met would do something about it.
"These are organised groups, some chaotic but generally organised, who are extremely violent and committing crime in areas of London. That needs to be dealt with in a systematic way."
