'No savings' from jail term cuts
Government plans to lock up fewer criminals will fail to cut costs or re-offending, a former Home Office criminologist said.
Professor Ken Pease said "community sentences as currently delivered have no evident effect on rates of reconviction".
Using them to replace short prison sentences simply "freed the group most likely to reoffend to do so sooner, with no evidence of a current treatment benefit from community sanctions to offset that", he said.
In his report, Prison, Community Sentencing and Crime, released on Friday by the think-tank Civitas, Prof Pease said it was important for any move away from the use of custody "to be based on something more than short-term political exigency".
His comments come after one of Britain's most senior police officers spoke out against Government proposals to lock up fewer criminals.
Metropolitan Police Commissioner Sir Paul Stephenson said he was "rather fond of villains going to prison" - including for crimes such as burglary which can carry sentences of less than 12 months.
Justice Secretary Kenneth Clarke questioned the link between rising imprisonment and falling crime earlier this year, saying it was "virtually impossible" to rehabilitate offenders on short sentences.
"Banging up more and more people for longer without actively seeking to change them is what you would expect of Victorian England," he said.
The Government launched a full review of sentencing policy, with Mr Clarke seeming to favour a greater emphasis on community sentences rather than putting more criminals behind bars.
He called for a "rehabilitation revolution", with sentencing policy focused on targeting the causes of reoffending. But his comments on the criminal justice system provoked anger among some Tory backbenchers.