This may seem extreme, but look at Singapore, which still operate under old British Law, now Gang members, would get even more extreme punishment, than the my suggested idea.
Gang culture is out of control, my self who has been robbed at gun and knife point several times, by Afro Carribean and Somali minorites, and I was lucky. So many parts of London are no go zones, these people seem to be above the law, and distill fear into the public.
I know some people are forced into the culture, and often there is not a way out, without danger to thier/familes life, but these cases are a minority. I do not accept that, the idea, there is nothing to do for young people, not enough activity centers. Often it is a case of getting respect, and having a status of importance, is, unfortunately the case.
Without diverting, and talking about Drugs, which is a huge aspect, but I should mention the problems with the Turkish/Kurdish conflicts, and the heroin culture, this is a serious problem, and often they really do seem rule their own roost. I can't say it hasn't been well documented.
I do have fear, for foreign visitors, when the Olympics arrive, especially for the Aquatics centre near Stratford.
A time, where you can walk the streets, feeling safe, in any part of London, seems like long dream away.
It is almost impossible to change the moulding of society, crime will never be wiped out completely. Unless we go into the unhuman realm of behaviour modifacation, then it will always seem to be a loosing battle.
But tough extreme laws, for extreme crime and disorder are needed. Laws and punishments are supposed to match the seriousness of the crime. Somewhere laws need to be changed.
How about Underground Military prisons, for the really serious crimes? They exist round the world, extreme measures, really do need to be taken.