Economist Richard Layard first proposed the idea of happiness as a way of measuring the success of a country 15 years ago, and now he feels it’s an idea whose time has really come. In his rousing new book Can We be Happier?, he lays out the evidence, principles and science behind initiatives for teachers, managers, health-workers and politicians to increase happiness in their spheres of influence – and argues that with measures such as these, we can turn away from destructive competition and transform our society. In conversation with Alex Clark, journalist, critic and broadcaster