Prisons are being stretched to breaking point by the huge increase in "ferocious and unjust" indeterminate jail sentences, penal reformers have warned.
A report by the Prison Reform Trust called on ministers to review the law, which allows prisoners to be held as long as they are deemed to represent a danger to the public.
The sentences, which have no fixed release date, were introduced in 2004 to deal with some of Britain's most dangerous offenders.
But the trust's report said more than 3,000 indeterminate sentences have been passed over the past two years. It said that figure was expected to increase to more than 12,000 by 2012.
The report said the sentences were in effect life jail terms that could be imposed for a list of 150 different offences. It said the sentences were being used for "relatively minor" offences rather than the hardened repeat offenders for whom they were designed.
The report accused ministers of playing "gesture politics" and ignoring the "operational chaos" caused by increasing prison numbers.
Last week Jack Straw, the Secretary of State for Justice, announced an urgent review of the sentences, known as "indeterminate sentence for public protection". Speaking after visiting Belmarsh Prison, Mr Straw said he was aware of concern from the judiciary, prison staff and prisoners.
Last month, ministers were forced to order thousands of non-dangerous prisoners to be released early to ease prison overcrowding after the number of prisoners hit record levels.
Yesterday Juliet Lyon, director of the trust, condemned the indefinite sentences as "Kafkaesque" and accused the Government of "recklessness". She said: "They were designed as a technical measure to detain a small number of dangerous offenders.
"But badly drafted, and whipped up by the previous Prime Minister and Home Secretary, they have become a ferocious, unjust law that, in two years, has catapulted around 3,000 people into jail for who knows how long.
"This is the Kafkaesque nature of modern day imprisonment."
Anne Owers, the chief inspector of prisons, has expressed concern at the number of indeterminate sentences passed. She said said the law did not take into account the massive amount of extra resources needed to care for such prisoners.
"There was no plan about how the prison system - already overcrowded, already under stress - was going to deal with them."