BBC FourCrime, especially violent crime, is falling across the Western world. But you would never think that if you watch British television, where murder continues to be the preferred form of entertainment. Every week I read Mark Lawson’s theatre column and marvel at the range of topics addressed by today’s young playwrights: ­family, relationships, work, politics, technology, race, class and so on. Then I consult the ­schedules to see what is inspiring their ­television counterparts. And the answer, ­overwhelmingly, is crime. This week alone three new crime series opened. BBC1 had Happy Valley, featuring a kidnapping and a troubled female detective with a difficult family. ITV had Prey, in which a detective is wrongly accused of murder and pursued by his own