Serious offenders are being moved into low-security open prisons where they could easily abscond, an investigation found.
Armed robbers and sex offenders are among those held in what some say are unsuitably relaxed conditions at HMP North Sea Camp, Lincolnshire.
An undercover investigation by a serving prisoner revealed apparently lax security procedures as well as widespread drug and alcohol use.
A probation chief and former prison official said some of the inmates held there were unsuitable for a category D open prison lifestyle.
At least one inmate - an armed robber and arsonist - escaped by simply walking out while others answered his roll call, the investigation found.
Paul Hocking, former North Sea Camp head of security, told the programme some offenders had been transferred there "far too soon".
Harry Fletcher, of the National Association of Probation Officers, agreed that some prisoners posed too great a risk to be held in an open prison.
But the Home Office said open prisons play an important role in rehabilitating offenders and all those transferred to such conditions are risk-assessed.
The investigation, to be shown on Channel 4's Dispatches, was undertaken by prisoner Dafydd Evans.
The television executive was involved in an accident in which a 24-year-old motorcyclist died and last year was convicted of causing death by dangerous driving and given a three-year sentence.
