Jack Straw, the Justice Secretary, was criticised last night after official figures on prison overcrowding suggested that it cost almost £460 a night to hold a prisoner in a police cell.

The figure compares with the average of £77 a night to keep a male prisoner in a Category B, medium security jail, in 2006-07.

The new amount - more than 20 per cent higher than previously admitted – reignited the debate over jail numbers. Last year 60,953 prisoners were housed in police cells at a cost of £28 million as part of emergency measures when prisons reach capacity.

The Prison Service was forced to restart the measures – known as Operation Safeguard – after the prison population in England and Wales began to rise again last weekend.

Jenny Willott, the Liberal Democrat prisons spokeswoman, said that the bill to the taxpayer was too large. She said: “Rather than spending public money sensibly on our police forces and measures to reduce reoffending, the Government is squandering millions on desperate attempts to find places to house prisoners.”

A Ministry of Justice spokeswoman said that the cost was not rising, but that the latest figures were based on a more realistic assessment of actual costs incurred.

Juliet Lyon, from the Prison Reform Trust, said the figures highlighted the inappropriate use of police cells: “If the Government focused on investing in drug and alcohol treatment for addicts, court diversion schemes for the mentally ill and effective community sentences, we would see both prison numbers and crime falling.”

The Government suffered more embarrassment when a leaked document appeared to show that officials are planning to force people to apply for ID cards. It states: “Various forms of coercion, such as designation of the application process for identity documents issued by UK ministers (eg, passports) are an option to stimulate applications in a manageable way.”

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