The United States is by a long chalk the most punitive democratic society. Two and a half million of its citizens are in jail – one in every 100 adults. The United Kingdom, no slouch in the punishment stakes and one of the most enthusiastic lockers-up in western Europe, has 84,000 prisoners. If the UK matched the US, its prison population would be 500,000. A hugely disproportionate number of American convicts are black, and incarceration is undermining fragile communities.

One of the engines that drives the US numbers is the sentence of ‘life without the possibility of parole’, handed down not just for heinous killings, but also under ‘three strikes and you’re out’ laws under which relatively small-time (usually very sad) young people, often involved in drugs,