The prison population keeps increasing

"That message is: imprisonment only when necessary and for no longer than necessary."

Mr Blunkett said he had made it clear he wanted tough sentences and supervision for those committing dangerous, violent and sexual offences.

But he continued: "We must use prison in the most appropriate fashion, and prevent the overloading of the system to the point where it becomes impossible to manage the necessary educational, training and employment work which will avoid those leaving prison reoffending."

His comments are likely to be welcomed by the director general of the Prison Service, Martin Narey, who said last week that the situation is now "critical".

And Mike Newell, chairman of the Prison Governors Association, said magistrates courts should no longer have the power to send offenders to jail.

Mr Newell said too many of those who had committed less serious crimes were being locked up and that short sentences were worthless and clogged up the system.