Delme Rees spoke out after 1,750 inmates were allowed to go free on 10 September to ease an overcrowding crisis in UK jails – many of them were just 40 per cent of the way through their sentences.

He said: “The sight of offenders celebrating outside prisons because of their early release will horrify most law-abiding people. I think most of the public agrees that if you commit the crime, you should expect to ‘do the time’, and when this doesn’t happen, as we’ve seen recently, it undermines confidence in the justice system.”

Delme added that police officers will have spent weeks and months investigating incidents, gathering witness statements and evidence to secure convictions, and will feel undermined by the early release of prisoners.

“As we know, if an offender is off the streets they cannot reoffend. So, inevitably we will see further demands on our already stretched police service and our members picking up the additional risk,” the chair said. “I worry that judges may start being more relaxed when it comes to sentencing if they feel the capacity is not there is our jails. The Government must now urgently invest in prison capacity and managing offenders when they are released so they don’t go on to re-offend.”

Probation officers are usually given more than three months' warning to prepare services to help monitor and rehabilitate a serious offender. However, Napo, the probation officers’ union warned that its members had received as little as a week’s notice, on 3 September, in some cases, including some serious offenders.

It voiced concerns that the extra demand on probation officers will mean that some ex-prisoners will not be properly monitored and could slip through the net.

The Ministry of Justice (MoJ) said in a statement: “The government inherited prisons in crisis and on the brink of collapse. Had that happened, the courts would have been unable to hold trials and the police to make arrests.”

Offenders serving more than five years were not eligible for early release.