My America is the United States of my mother's childhood, when she was kissed at the age of 9 months by Grover Cleveland, in his successful presidential campaign of 1892. I was pleased to note that Barack Obama, another Democratic candidate, claims to have kissed several hundred babies in the course of the primaries to date: he will no doubt have to kiss a few hundred more before he gets to the White House.

Kissing babies is a splendidly politically incorrect thing to do. It is liable to spread germs; it could be misinterpreted as harassment. It marks out Senator Obama as a thoroughly old-fashioned candidate, however progressive he may be in his speeches. Compared with Hillary Clinton, it makes him seem a conservative candidate, though not as conservative as Senator John McCain, who is a 71-year-old war hero with a heart of gold. The United States could do with a return to the good old days, in idealism as well as campaign styles.

My grandfather was a native-born American, the son of Irish immigrant parents. He believed that the US was the land of equality, freedom and law. He became the president of the village of Mamaroneck because he understood the duty of the citizen in a democracy. He hoped post-Civil War America would continue to move towards greater equality, of immigrants and native born, of black and white.

Last week there was published a report that he would have found very disturbing, as indeed would my mother. This report concerned the American prison system; it was published by the Pew Centre, a Washington think-tank. The figures are shameful for anyone who feels a loyalty to the American tradition.

The big figure is that one adult American in 100 is currently in prison; that compares with one in five or six hundred in Britain. The annual budget for US prisons come to $50 billion. The situation is particularly bad among young black males. About 11 per cent of young black men are in prison.

This has been defended on utilitarian grounds. Jeremy Bentham, who coined the phrase “the greatest happiness of the greatest number” as the justification for social action, was himself a designer of prisons. His prison was actually built on the Millbank site that now houses the Tate Gallery. It did not work, but sent the prisoners mad.

The Sunday Times yesterday had a bizarre quotation from a Benthamite law professor from Utah, Paul Cassell. He argued that the Pew Report has “ignored the very tangible benefits” from reduced crime rates of jailing people. “It's terrible we have to incarcerate so many so the rest of us can live safely,” he said, but that's the price of living in the freest society in the world. If one in 100 in jail is a sign of the most free society in the world then China, with a prison population of 1.5 million in prison, is the runner-up in the proportional prison population and presumably in freedom.

There is no real evidence that “prison works”. Most European countries have lower prison rates and lower crime rates than Britain, let alone the United States. In America, New York has one of the best recent records in reducing crime. Between 1993 and 2006 the violent crime rate in New York fell by 59 per cent. At the same time the prison population was reduced by 2 per cent. Success may be due to sending the right people to prison - those who are a real threat to society - and to good policing.

Nearly half the federal prisoners in the United States are in jail for non-violent drug offences. Drug offences are particularly common in the slums of the big American cities, as in Britain. They are associated with the low standards of inner-city schools, with gangs that often are violent, and with limited job opportunities.

Barack Obama is himself a relatively young black man, who was reared by a single mother and by his grandparents. He took the middle-class professional route out of poverty. He went to Harvard and was Editor of The Harvard Law Review, a post of high prestige. Yet his childhood and youth may never have been more than a minor slip away from social disaster. More than one in 10 of his black contemporaries did not reach Harvard; instead they were sent to the penitentiary. Perhaps he will be able to do something about that, if he is elected. I'm sure he will try.

The United States is a vast country, with widely varying standards in almost everything, including American law. American lawyers do undertake public service legal actions, but, in general, the best US law is the most expensive.

Conrad Black's case is an example. Lord Black of Crossharbour is expected to go prison today, though his lawyers have demolished several charges against him. He was convicted on plea bargaining evidence that probably would have been excluded in a British court; there is an obvious danger of injustice when a witness can benefit by a shorter sentence if he incriminates a colleague. Conrad Black's defence has cost him $60 million so far, a sum beyond the means of all but a tiny number of super-rich families.

If Barack Obama had been charged with a drugs offence in his early twenties - and he admits to drug use - he would not conceivably have had $60 million to pay for his defence. He would not then have been able to raise $1 million. Young blacks in prison in the United States could not possibly afford the best available defence. They are victims of American society, even though they may also be criminals.

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