Gordon Brown repeatedly defended the prisoner early release scheme today amid accusations from the Conservatives that violent offenders have been released early.
The prime minister insisted no prisoner serving a sentence for a serious violent crime had been released early.
The government set down 15 conditions for early release, Mr Brown reminded his opponent, and each case had been judged against them.
Mr Brown was responding to allegations from Mr Cameron that probation officers had raised concerns over some of the prisoners selected for early release.
In a prime minister's question time domination by law and order, Mr Brown said the government would increase the number of prison places to meet demand.
An additional 1,800 prison places have been confirmed on top of the 8,000 already planned, meaning prison capacity will reach 90,000 in the coming years.
However, he refused to rule out the need to retain prisoner early release as a permanent measure.
He downplayed the significance of the scheme, saying prisoners are only released 18 days early.
The prison population has risen as a result of the government's policies on crime, Mr Brown insisted. While crime has fallen, sentencing for serious offences has increased, the prime minister explained.
In his strongest PMQs performance to date, he told Mr Cameron crime doubled under the last Conservative government, the number of police officers fell - and the shadow chancellor has now said there can be no more money for crime and policing.
"He said he was the future once and all he can do is talk about the past," Mr Brown said.
In a written statement earlier this week, prisons minister David Hanson said more than 1,700 prisoners have been released early during the first week of the scheme, of whom 1,227 were serving a sentence for six months or less.
The justice secretary admitted 30 criminals freed early have broken the terms of their release, including committing fresh crimes.
12 of these have since been returned to jail while 18 are on the run.
Of the 30, six have committed a fresh crime and seven were reported for bad behaviour. 11 failed to report to a probation officer and six were not living at their stated address.