Knife crime is at a nine-year high. Everyone agrees: something must be done. Some politicians want more police on the streets, or tougher sentences. Others want cuts to mental health services to be reversed. One MP has suggested every knife in Britain should have a built-in GPS tracker – good luck with that. But knife crime it is a complex issue, and young people’s lives depend on policymakers getting it right. So today, Ayeisha Thomas-Smith is taking a big-picture look at the issue with one of the journalists who’s covered this issue more than perhaps any other: the Guardian’s editor-at-large, Gary Younge.