By Dominic Casciani
Home affairs reporter, BBC News
The prison population in England and Wales is currently at a record high
Powers to jail inmates indefinitely have created a "perfect storm" as the prison system has struggled to cope.
Prisons watchdog Anne Owers attacked indeterminate sentences for public protection, saying their scope and impact had damaged the penal system.
Her joint report with the probation inspectorate said the law's introduction was a lesson in "how not to" tackle offenders.
There are some 4,200 inmates on the sentences, according to figures.
Indeterminate sentences for public protection, known as IPPs, came into force in April 2005.
They gave judges the power to jail a serious offender for a specific term - but order that the criminal remains behind bars until they have proven they had reduced the risk they posed.
But in their joint report, the prisons and probation inspectorates said that IPPs would affect the criminal justice system "for years to come".
Ms Owers said that by the time the courts started to use the new sentencing powers, the prison population was already "surging".
"This large number of new, and resource-intensive, prisoners was fed into a system that was already under strain," she said.
"This has not only increased pressure, and reduced manoeuvrability, within the prison system; it has also meant that a great deal of officials' time and energy has been taken up with simply finding enough prison spaces."
The joint report said the arrival of IPPs coincided with a weakening of systems designed to manage prisoners serving a life sentence.
At the same time, the Probation Service was under-prepared and resourced for its critical role in deciding which of these inmates should remain inside or be released.
In turn, many IPP inmates on relatively short sentences remained behind bars, further adding to record population pressures.
"This was a perfect storm," said Ms Owers.
"It led to IPP prisoners languishing in local prisons for months and years, unable to access the interventions they would need before the expiry of their often short tariffs."
The report revealed that one prison governor described the effect of all of this was akin to the government doing its shopping without first having a fridge.
Justice Minister David Hanson said the sentences were "vital" to protect the public.
"We have already identified many of the shortcomings raised in this report which was undertaken a year ago and work is being carried out to address them.
"We have made clear on a number of occasions that the IPP sentence was never intended to be used generally for short tariff prisoners.
"We now have legislation in place to ensure the sentence is used as intended."
But Juliet Lyon of the Prison Reform Trust accused ministers of "acting tough, not smart" to chase headlines.
"Despite some changes, it is likely that many of these prisoners who have served their minimum tariff but remain in prison do so because they have had no opportunity to demonstrate they pose no risk, if released.
"Ministers cannot abandon these people in a maze with no exit and must act quickly and decisively to put things right and prevent more costly legal challenges."
Erica Restall, of Switalskis Solicitors, was involved in a High Court test case involving Brett James who was detained for longer than his tariff under an IPP sentence.
He was jailed in 2005 with a minimum tariff of one year and 295 days for a violent attack on a man near Wakefield. His sentence expired in July 2007, but he was not released until February 2008.
Ms Restall said: "In Brett's case he did not even get to take the first step and undergo assessment for the courses he would need to complete to show that he posed a reduced risk."
James was held at Doncaster Prison, and while Ms Restall says he was a model prisoner and completed as many courses there as he could, none of it would count with the parole board.
She said: "It was a huge frustration for him, and very demoralising. Going into prison was a huge shock to him and throughout his time he was impeccably behaved and tried to access as many courses as he could to show he was attempting to better himself.
"Yet he watched other people come and go under different sentences and that was hard, although he always accepted the seriousness of his crime."
Ms Restall said IPP sentences will cause ongoing problems while there is insufficient access to assessment and subsequent courses for inmates to present appropriate evidence to the parole board.