The Times last Saturday...sorry, I can't provide a link as the material is behind a pay-wall...published a two-page spread with the headline, "Violent crime is surging four times as fast outside London."
Certainly, knife-crime is only one aspect of violent crime, but you surely have not failed to hear of the recent escalation in knife-killings in Birmingham and other midlands and northern cities.
Any attempt to lay this phenomenon at the feet of the Mayor of London is nothing more than a pathetic attempt to score a political point. Even worse, in a way, is how it has now started to be all right to blame head teachers for having disruptive pupils, who then join knife-gangs, expelled.
Let's blame anything and anybody but the true culprits, the government and their police-numbers reduction policies, seems to be the order of the day.