Lord Judge wants the effects of possible sentencing changes assessed
Increasing jail terms for criminals should not be proposed without calculating how much it would cost, a senior judge has warned.
The most senior judge in England and Wales, Sir Igor Judge, cited prison overcrowding and "under-resourcing".
Last week the government said minimum sentences for knife murders may change.
Following the murder of London teenager Ben Kinsella, concerns were raised that the tariff for gun murder was 30 years, but just 15 years for a knife murder.
Writing in the Sentencing Guidelines Council's annual report Lord Judge, the Lord Chief Justice, said ministers should publish estimates of the likely bill to the taxpayer before changing sentencing law.
He said the government had "under-resourced" prisons when introducing indefinite terms for dangerous criminals in 2003, with "potentially alarming" consequences.
The creation of the sentence led to a surge in the prison population.
The government releases early about 2,500 prisoners a month to ease overcrowding.
Lord Judge said: "Before legislative decisions about criminal justice and sentencing policy are made, the consequences in terms of financial cost and other pressures on the system should be assessed and the results made available for public consideration.
"If this practice had applied when, for example, the provisions for imprisonment for public protection in the Criminal Justice Act 2003 were under consideration, the potentially alarming consequences of under-resourcing may have been avoided."
The Sentencing Guidelines Council, which he chairs, issues advice to judges about what sentences should be handed out for different crimes.
Last week Justice Secretary Jack Straw said he would examine the minimum term "starting points" for people convicted of murders involving knives in England and Wales.
But the Conservatives said the review was little more than a "public relations exercise".
The debate took place in the wake of the trial of three men convicted of murdering Ben Kinsella, 16, as he fled a fight in north London in June 2008.
Mr Straw had been responding to a question from Labour backbencher David Winnick, who told the Commons that the jail terms handed down to Ben's killers were "not really sufficient".
Michael Alleyne, 18, Juress Kika, 19, and Jade Braithwaite, 20, all from London, were all given life terms with a minimum 19-year tariff.
Ben's parents, George and Deborah Kinsella, said the government should review sentencing guidelines to enable judges to hand down stiffer sentences.
Mr Straw told MPs he recognised there had been "considerable concerns" about the gap between minimum terms for gun and knife murders.
He added: "In the light of these concerns I intend to review the provisions of schedule 21 of the Criminal Justice Act 2003 with a view to deciding whether to amend it as I can by order."
He said he would also consult the senior judiciary and the Sentencing Guidelines Council and would be "very happy" to receive other representations.