The Prime Minister's "tough but intelligent" approach to a rehabilitation revolution risks being undermined by overcrowded prisons and budget cuts, campaigners have warned.
David Cameron said all but a small number of high-risk prisoners will receive help to turn their lives around and break the cycle of reoffending by the end of 2015.
But the long-awaited speech comes after Chief Inspector of Prisons Nick Hardwick said politicians wanting a rehabilitation revolution faced a stark choice - "reduce prison populations or increase prison budgets".
He highlighted conditions at Britain's largest jail, Wandsworth prison in south west London, where excellent workshop facilities stood empty while prisoners watched TV in their cells because there were no resources to move offenders from one to the other.
Vicki Helyar-Cardwell, director of the Criminal Justice Alliance which represents almost 70 organisations, said prison overcrowding and budget cuts mean that rehabilitation is being undermined.
Mr Cameron admitted there was "no blank cheque" and there was "much less money than there used to be".
But he said the Government's ambitions could still be realised through intelligent reforms.
Speaking earlier on a visit to Wormwood Scrubs prison in west London, Mr Cameron said: "We have got to do more for less.
"Every place here costs £40,000, there are 600 staff that work in this prison - it's not a shortage of money, it's that we haven't been focusing people on what really matters, which is the results."