So what really works? Treatments in jail do some good, but it's mostly too late: finding a family and a job or just growing older make most prisoners eventually give up crime.

It is now possible to quantify people's levels of happiness pretty accurately by asking them, by observation, and by measuring electrical activity in the brain, in degrees from terrible pain to sublime joy.

Is anyone serious about the politics of happiness? David Cameron dipped a toe in the water, using the word lightly, but denying the hard policies it implies. Labour shies away from it, but should take up the challenge.

Polly Toynbee Quotes