Last week we saw more reports of stabbings of young people in London, which are part of a distressing number of violent attacks in major cities across the UK. Each attack represents numerous personal tragedies. A child, relative, friend taken away too soon – a lifetime of potential never realised. But in the offender there is also a tragic case – someone who has chosen a path that devastates not just the life of their victim but also their own.

­After such a serious attack hits the headlines, we – politicians on all sides, police, experts – come forward to express our concern, and put forward competing solutions. But while debate is necessary, it is not enough. Tackling violence on our streets...