Rise in prison numbers unsustainable, says justice secretary, who blames media for creating image that prison life is easy

The rate of jail sentencing is "financially unsustainable", the justice secretary, Kenneth Clarke, has said, delivering a defiant riposte to critics within his own party and the tabloid press who have suggested that his plans to overhaul the penal system are soft on crime.

Clarke last year unveiled a green paper on sentencing as part of government plans to cut the £4bn prison and probation budget by 20% over four years, promising to end a Victorian-style "bang 'em up" culture and reduce high reoffending rates by tackling the root causes.

But after facing sustained criticism, he used an interview with The Times to dismiss characterisation of him as a minister who is "soft on crime."

He is preparing to publish a bill next month which will include proposals to allow for large sentence discounts in return for early guilty pleas and diverting the mentally ill away from jail. The goal is a 3,000 cut in the record 85,000 jail population in England and Wales in four years.

"[The rise in prison numbers is] financially unsustainable. That is not my principal motivation but it is pointless and very bad value for taxpayers' money," Clarke said.

He blamed the media and lobby groups for helping to create a public perception that prison life was easy, adding: "Prisons are not hotels, they are not comfortable, they are overcrowded, they are noisy. Anyone who visits a prison soon realises the prevailing atmosphere is one of stupefying boredom on the part of inmates.

"It is just very, very bad value for taxpayers' money to keep banging them up and warehousing them in overcrowded prisons where most of them get toughened up."

He said that too many prisoners sit idly in their cells when they could be doing something more productive with their time. "I would like to see prisons where there is a working environment, where people get into the habits of the rest of the population."

Private firms would be encouraged to operate in jails and help endow inmates with skills that would make them employable when they entered into free society again.

"The firms are cautious about advertising it because the newspapers write them up as 'employing jailbirds'," he said.

However, Clarke did pledge to make community punishments tougher by insisting offenders do unpaid work for eight hours a day.

"I want them to be more punitive, effective and organised. Unpaid work should require offenders to work at a proper pace in a disciplined manner rather than youths just hanging around doing odd bits tidying up derelict sites," he added.