The National Association of Probation Officers (Napo) claims that some of the most hardened criminals were set free without any supervision. It also says 29 per cent have already reoffended, compared to the usual rate of 8 per cent.
Other prisoners from the group are turning up in magistrates' courts across the country for burglary, theft and deception, since the Prison Service decided it had miscalculated how long they should spend behind bars. The releases were halted after Michael Howard, the Home Secretary, took legal advice.
The 32-year-old sex offender, also a drug user, was not due for release until Christmas. But the first the family of his victim knew of his early release was when they saw him in a shopping mall on the day he was set free. He is currently living in a cheap hotel where he faces eviction for not paying his bills.
Another sex offender, who had abused children, had been due for release only on the condition he resided at an assigned hostel under strict supervision. Instead he was released two-and-a-half months early with nowhere to go.
Harry Fletcher, assistant general secretary of Napo, said: "This is a picture of complete chaos, and it will be the probation service and the public picking up the pieces. Clearly some of these prisoners are dangerous and they are under no sort of supervision.
"Somebody at least managed to get hold of the victim's family to tell them, but there was total panic. They started changing all the locks on their doors. A place was eventually found for him, but it was too late, the damage has been done.
Napo studied the fate of 80 prisoners in 12 districts across Britain, who were released with only a few hours notice and a discharge cheque for pounds 46.75. Many were set free by the time probation offices had closed for the bank holiday weekend, and the association estimates up to 50 per cent of unsupervised former inmates will reoffend.
One prisoner in his 40s ran up a hefty hotel bill in North Wales before being arrested for deception and being sent back to prison; another threw bricks through a police station window out of frustration at failing to find a place to sleep.
Another 24-year-old former prisoner was due to enter a drug rehabilitation programme, but the place was not available when he was released early. Instead he was arrested for burglary in an attempt to raise money to buy drugs, and has forfeited his place on the scheme.
The probation service was given three hours notice of the release of another 20-year-old heroin addict. They tracked him down three days later when he appeared at in court on several charges of shoplifting.
Other prisoners with records of serious offences have completely disappeared. A 27-year-old man released in Lancashire failed to turn up for a second meeting with probation officers after it emerged he had been in prison for kidnapping women, violent crimes against women and possessing fire- arms.
Bob Thomas, a spokesman for the Prison Service, denied yesterday that the former prisoners were reoffending at an unusually high rate, and insisted that the probation service should have been aware of all those who had been released. He said: "There may have been some who have slipped through the net, but all these prisoners were due to be released anyway. Unfortunately reoffending rates are high, and I simply do not accept that these figures are much more than usual."