Tough sentencing by judges, rather than a rise in crime, has led to the record prison population, research has found.
The prison population has increased by 71% since 1991
The 71% rise in the prison population between 1991 and 2001 was due to a "misplaced emphasis on toughness rather than effectiveness" as courts sentence more people to prison and for longer terms, according to a report by the Prison Reform Trust.
It found that the idea that courts were lenient on criminals was a myth but the "increasingly punitive climate of political and media debate about crime and punishment" had fuelled higher sentencing.
"The courts will continue to make ever-increasing use of prison unless this climate of opinion changes, and clear and consistent political leadership is needed to make this happen," the report said.
It said courts needed to be told to use imprisonment less and where custodial sentences were set, they should be shorter.
If you have a silly slogan like 'Tough on crime, tough on the causes of crime', of course sentences are going to go up
Sir Oliver Popplewell
A retired high court judge told the BBC the government had itself to blame for the rise in prison numbers.
"If you have a silly slogan like 'Tough on crime, tough on the causes of crime', of course sentences are going to go up," said Sir Oliver Popplewell.
"You can't at the same time then start complaining that the prison population has increased," he told BBC Two's Newsnight.
Lord Dholakia, chairman of the National Association for the Care and Resettlement of Offenders, said the slogan had "skewed" the sentencing debate.
England and Wales prison population is 73,478 - highest ever level
UK has highest imprisonment rate in the European Union at 139 per 100,000
Home Office predicts a prison population of between 91,400 and 109,600 by end of decade
Ninety of the 138 prisons in England and Wales were overcrowded by May 2003
Of 13 prisons opened in the past 10 years, nine were overcrowded at the end of May
Source: Prison Reform Trust
He said the system of criminal justice had been "ratcheted up" so judges had become much tougher.
The report's lead author, Mike Hough, said it was "perverse" that sentencing policy was driven by misunderstanding.
"Ten years ago, people thought that the courts were far too soft on crime.
"Judges and magistrates have responded by getting progressively tougher. But the public simply haven't realised this, because they haven't been told clearly enough."
Prison Reform Trust director Juliet Lyon said: "It is time to bring a sense of proportion and fairness back into sentencing which has become grossly inflated by a misplaced emphasis on toughness rather than effectiveness."
Prisons Minister Paul Goggins agreed that the government had a policy of tougher sentencing, but said it was coupled with community sentences for lesser crimes.
"That would reserve prison for the people who really need it," he told Newsnight.
Researchers at South Bank University's Criminal Policy Research Unit found that since 1991 overall crime rates and the number of offenders appearing before the courts have both fallen, yet the prison population has risen.
Sentencing trends had changed in the past decade, with a petty thief three times more likely to go to prison now than in 1991, and the chances of being imprisoned by a magistrate for driving while disqualified has almost tripled.
Burglars and sex offenders also receive much longer jail terms than they did in 1991, with the number of offenders being sent to jail for four years or more increasing by 62%.
In interviews with 133 judges and magistrates from across England and Wales, the researchers discovered how they were influenced when sentencing.
'Harsh' legal framework
As well as the political and media debate, "a harsher legislative and legal framework" influenced them.
While many judges and magistrates are "generally happy" with the range of non-custodial options available, they are concerned the Probation Service is under-funded.
Community sentences that include the provision for regular court review, such as drug testing and treatment orders, are particularly favoured.
The Lord Chief Justice, Lord Woolf, said the report showed there was a way to reduce the prison population.
"The answer is a change in rhetoric from all those with a leading role in the criminal justice system."