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.

Could a government dare to set out with happiness as its goal? Now that there are accepted scientific proofs, it would be easy to audit the progress of national happiness annually, just as we monitor money and GDP.

Inequality makes everyone unhappy, the poor most of all, and that is well within the remit of the state. More money gives less extra happiness the richer we get, yet we are addicted to earning and spending more every year.

But the single overwhelming reason why jails are bursting is longer sentences given for more crimes.

Thresholds of pain, indignity and incapacity are entirely personal.

Crime is only the worst example, but it is a paradigm for other Labour policy disasters. No one tells the voters that crime is falling: let them stay scared senseless.

Working lives are for the state to influence. Unemployment makes people unhappy. So does instability.