On sunny afternoons, having collected the kids from school, I am sometimes coerced into making a minor detour through a nondescript North London park. The equipment is meagre and battered; there are so many stone steps and steep drops that the place resembles a game of Tomb Raider and, as nothing overlooks the playground, it is both a doggy convenience and a youth hangout. Today, there are eight or more teenagers, mostly in hoodies, being noisy on the swings. Two women from a local action group are bravely asking the youths how the park could be improved. Then, politely, I...