I think that is the only short term measure available. Sir Ian Blair has said that his force now has a policy to charge people found in possession of a knife, rather than issue cautions. Recently, the percentage of people being charged has gone up from 40% of those arrested and found to be in possession, to 95% (in the past week). You could ask, "Why only take action recently?", but I guess one of the upsides of the media reporting/hype is politicians and police authorities are pushed to take action against an existing, serious problem. Addressing the youth end of the problem, Campaigns, and Facebook groups, and all the rest of it may have an impact if they can generate an allied feeling that, not only will you be charged and facing prison if caught, but your peers think it uncool and unacceptable to carry a knife. Seems a long road to travel, however.