Prison overcrowding is undermining the rehabilitation of prisoners and risks increasing reoffending in the future, a report has said.
The Criminal Justice Alliance, which represents more than 60 organisations, called for the Government to urgently limit "the unnecessary use of prison, ensuring it is reserved for serious, persistent and violent offenders for whom no alternative sanction is appropriate".
It comes after Chief Inspector of Prisons Nick Hardwick said the rising pressure on prisons from budget cuts and increasing numbers cannot go on indefinitely.
The prison population in England and Wales hit 87,787 on Friday, less than 400 from the all-time high of 88,179 set last December and 98% of the usable operational capacity.
"When prisons are overcrowded, the risk that offenders will commit crimes upon release may even be greater," the report said.
A combination of "strain on prison staff, reduced access to educational and training programmes, and lack of mental health and substance abuse treatment services ... reduce the likelihood that prison sentences will actually work to tackle the causes of offending behaviour", it said.
Vicki Helyar-Cardwell, the group's director, added: "Overcrowding has, all too often, become an accepted part of life in prison, but while the system is just about coping, it struggles to meet the challenges of unexpected surge, such as those that followed the riots last year."
Judges handed out sentences almost four times as long for those convicted over the riots compared with those guilty of of similar offences in 2010, Ministry of Justice figures showed.
A Ministry of Justice spokeswoman said: "Prison is necessary for the most serious and persistent offenders.
"There are sufficient places for those being remanded and sentenced to custody and we are keeping the prison population under careful review. In the next couple of months, two new prisons are due to open which will increase the overall capacity by around 2,500 places."