Britain’s most senior judge has given warning that the shortage of prison spaces was now “critical” as a result of ministers’ failure to take account of the cost implications of their sentencing policies.

Lord Phillips of Worth Matravers, the Lord Chief Justice, said that the present prison overcrowding could not continue. And he delivered a stark message to ministers — either they should fund the sentences that judges impose or change the sentencing framework that requires them, often, to jail offenders.

“We are in a critical situation,” he said. “The prisons are full to capacity.” Prisoners who went to court did not know if they would return to the same cell or even the same prison. Cells designed for one were being used for two and prisons were being forced, literally, to close their doors to more admissions. “Prisoners are being driven around for hours on end in a desperate search for a prison that can squeeze them in,” he added. “As often or not 200 or 300 are spending the night in police or court cells. We simply cannot go on like this.”

He said that Parliament had not been prepared to leave it to judges to decide if an offence merited imprisonment and, if so, for how long. Instead, it had set down how the seriousness of an offence should be judged, as well as starting points for minimum terms to be served for murder in the Criminal Justice Act 2003.

The result, he said, was to “increase very substantially the terms of imprisonment to be served, not merely for murder but for a whole range of other offences that must logically bear a relationship to the sentences imposed for murder”.

Delivering a lecture to the Howard League on Penal Reform, Lord Phillips added that it was not clear that this result had been intended and “even less clear” that it had been costed. “If you decide to lock up one man for a minimum term of 30 years, you are investing £1 million or more in punishing him.

“That sum could pay for quite a few surgical operations or for a lot of remedial training in some of the schools where staff are struggling to cope with the problems of trying to teach children who cannot even understand English.” He said that if there was no change in prison lengths or the proportion of offences that resulted in jail, prison numbers would rise to 95,000 in 2014.

Money spent on keeping offenders in prison by way of punishment was money that could be spent on rehabilitating them in the community, he added.

“Unless Parliament is prepared to provide whatever resources are necessary to give effect to the sentences that judges choose, in their discretion, to impose, Parliament must re-examine the legislative framework for sentencing.” He urged some way be found of linking resources to the setting of the sentencing framework within which judges work.

A public debate was needed on the issue, which should look at the extent to which resources should be given not just to imprisonment but other types of sentence that aim both to punish and rehabilitate, he said.

But that could happen only if those taking part put aside the chance to score political points.

Lord Phillips also called for community sentences to be made more effective, which was not the present perception of the public or the media.

And he called for all judges and magistrates to do a stint of community service, as he did for a day, working with a team cleaning and repainting an underpass. “I found it a positive experience,” he said. But the attendance rate for such projects was “depressing”, at 60 per cent. Team leaders should ensure that their teams turned up, he said.

He added that it would be “no bad thing for judges or magistrates and others involved in the criminal justice system to spend the odd day working with the teams, not incognito as I was, but as volunteers joining in a worthwhile community activity”. Such sentences, or community payback, were a desirable alternative punishment to prison; it was cheaper; was a visible form of restorative justice; and more likely to achieve rehabilitation than short prison terms.

Lord Phillips also went on to criticise the interderminate sentences for public protection, which judges had to impose for a large number of offences where, according to the Act, the offender was dangerous.

The sentence also put a heavy demand on prison resources and an increased burden on the probation service and Parole Board.

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