A REPORT showing that one in 100 Americans adults is in jail - five times the rate in Britain - has prompted a fierce debate between those who believe the record prison population has led to declining crime rates and those who say the system’s £25 billion annual budget could be better spent.

The Pew Centre on the States, a Washington think tank, says the number of adult prisoners has tripled since the 1980s to 2.3m - close to the population of Greater Manchester.

Susan Urahn, a senior Pew researcher, said the US now held one in four of the world’s prisoners. China was second, with 1.5m people behind bars. There are 82,000 people in jail in England and Wales, or roughly one in 500 adults. The proportion is similar in Scotland and Northern Ireland.

In some cities, young black men are said to be vanishing from the streets because of a combination of jail and recruitment by the armed forces. According to the Pew report, one in nine black men aged between 20 and 34 is in prison.

Urahn said jailing so many people was not worth the price: “Being seen as tough on crime is an easy stance when you have the money, especially during the 1980s and 1990s, when we built a lot of prisons. But now it’s not only blowing a hole in budgets, it’s not showing a return on the money we spend - in some states, more than on education.”

Nearly half of federal prisoners are serving time for nonviolent, drug-related offences, a number that increased as sentences grew longer in the 1990s. The introduction of the “three-strikes” rule, where criminals are jailed for life after a third offence, has also swollen prison numbers in states such as California.

Some criminologists say prison works particularly well for career criminals by simply keeping them off the streets. Paul Cassell, a law professor at the University of Utah, said the Pew report had looked only at the costs and ignored the “very tangible benefits” from lower crime rates across the country.

“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 most free society in the world.”

Between 1993 and 2006, Florida sent 75% more people to prison and its violent crime rate fell by 41%. Yet in the same period, New York’s prison population fell by 2% and its violent crime rate dropped by 59%.

Experts say that was because New York recruited more police to guard poorer areas and treated more nonviolent drug users as addicts rather than criminals.

Even in cities with acute drug problems, such as Baltimore, local leaders have been seeking ways to cut its budget-busting prison population.

“It is to our shame that we have the highest incarceration rate in the world, including despotic countries like Cuba,” said Curtis Anderson, chairman of Baltimore city council. “But inertia is keeping people in jail when they should be in treatment. I hope this report helps.”

The report has been condemned as “inaccurate and naive” by members of the prison officers’ union, which has grown into one of the most powerful unions in the US over the past 30 years. In some rural areas, the local prison is the only employer.

The union cited statistics from the Department of Justice, which show prisoners as a proportion of the total population rather than just adults. “The real figure of the incarcerated is one in 130 people,” it said.

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