Three prisons will be closed with the loss of almost 850 places in moves that sparked warnings of unrest in jails – and disagreement within Tory ranks.
Justice Secretary Kenneth Clarke yesterday confirmed reports that Ashwell prison in Rutland and Lancaster Castle, Lancashire, will be closed by March.
A third jail, Morton Hall women's prison in Lincolnshire, will be turned into an immigration detention centre "as soon as possible", the Ministry of Justice (MoJ) said, with plans under way to move those held there.
Mr Clarke told MPs it was difficult decision but necessary. But the plans have been questioned, with warnings from the Prison Officers Association, while the Tory MP for Shipley, Philip Davies, complained of dismay within Tory ranks at Government reforms of the justice system.
Mr Clarke said: "Closing outdated and expensive prisons is an important step in our strategy to provide a secure and modern, fit-for-purpose prison estate, while improving efficiency and value for the taxpayer.
"The changes will reduce our current capacity by 849 places and I am confident that they can be safely managed within existing headroom, whilst maintaining our ability to cope with any increase in population."
There were 82,991 prisoners last Friday, about 5,000 less than the usable operational capacity of 87,936, MoJ figures showed.
Last month, Mr Clarke set out plans to reduce the prison population in England and Wales by about 3,000 over four years. These would see judges given more discretion over how long killers spend behind bars, more offenders handed fines or community sentences, and foreign nationals allowed to avoid jail as long as they leave the UK forever.
Mr Clarke said it is a "simpler, more sensible" approach but Tory backbenchers have voiced concern that criminals would avoid being sent to prison.
Yesterday he added: "Security remains our highest priority and we will ensure that this, along with efficiency and current performance levels, is maintained across the estate.
"Decisions on the future size of the prison estate will be driven by population demand and prisons will only close when capacity allows."
Prisoners will be moved to other jails and staff will be offered a "voluntary exit" scheme or moved to neighbouring establishments, he told MPs, adding that both Lancaster Castle, where the prison is in fact housed in a medieval castle, and Ashwell are not fit for purpose.
Morton Hall will be managed by the National Offender Management Service on behalf of the UK Border Agency.
But Conservative MP Mr Davies criticised the decision, saying: "I think this is incredibly premature and what Kenneth Clarke has proposed with regard to prisons is unacceptable, not just for the vast majority of Conservative MPs but for the vast majority of the public.
"Kenneth Clarke and the Government have to realise that they are in coalition with the Conservatives as well as the Liberal Democrats."
The Prison Officers Association said it was "dumbfounded at the crass decision".
In a statement it said Mr Clarke's insistence that security was the highest priority "has a hollow ring to it for prison staff and the public".
It added: "We have seen our members seriously injured on a daily basis, due to the loss of frontline staff through cost cutting under the guise of the rehabilitation revolution banner.
"In order to have safe, decent and secure prisons Mr Clarke, you need professional prison staff in place that feel safe, secure and are treated with decency."