All depends what you class as a gang, I think more than two can be classed as a crowd, so it really comes down to behaviour.
As for taking back the streets, thats easy, punishments to fit the crimes, and the will to carry them out, but while we have this misbegotten Political Correctectness, no chance.
Maybe we could all gather on the rooftops and make noises like baboons - that'd stop them. Or we could adopt an ex-IRA N.Ireland attitude towards anti-vigilsim and kneecap anyone who's breaking the law whilst we sell drugs and arms without a care in the world.
Seriously, I think organised, non-corrupt self styled 'law enforcement' would be beneficial to the UK. It would NEVER be sanctioned or supported by government or police because it would be a complete embarrassment to their shambolic and ineffective abilities to attempt to keep law and order whilst being viewed as a joke.
The main concern is amongst witch-hunts, poorly informed information resulting in the innocent getting a shoeing. Look at those idiots in Portsmouth a few years back who administered an attack on a paedatrician, thinking he was a paedophile! In the wrong hands it would be deadly....but in the right hands there'd be alot of petty theives, drug dealers, fraudsters and hoodies walking around with perpetual limps and the fear of being 'watched'