Record numbers of people are being held in prisons in England and Wales, government figures showed yesterday.
There are 85,076 prisoners – just over 2,000 under the capacity of 87,196 spaces, despite nearly 5,000 extra places being created in the past two years.
The new figures drew criticism from penal reform groups, who described the rise as very worrying.
Juliet Lyon, the director of the Prison Reform Trust, said: "The cost of sustaining our out-of-control prison population has gone beyond affordable bounds. Each new prison place costs £170,000 to build and maintain, and the cost per prisoner per year is £41,000."
Frances Crook of the Howard League for Penal Reform said leaders of all political parties must set out their policies to tackle a crisis in prisons.
She said: "This ceaseless growth in prison numbers is untenable and any new administration will have to bite the bullet and find a strategic way to reduce the prison population."
In February, the Justice Secretary, Jack Straw, announced the end of an early-release scheme which saw more than 80,000 offenders let out.
No prisoners were eligible for the controversial End of Custody Licence (ECL) scheme after 12 March and the last remaining ECL prisoners were out on 9 April.
The prison population has doubled since the mid-1990s and risen by 3 per cent in the past year.