The prison population is currently at a record high
A prisoner allegedly raped someone after being released early under a government scheme aimed at easing jail overcrowding, it has emerged.
More than 26,000 prisoners in England and Wales have been freed up to 18 days before their release date since the end of custody licence began a year ago.
The Ministry of Justice has revealed that four of them allegedly committed six sex offences - including one rape.
The ministry gave no more details on the alleged offences.
But it said any offending was "regrettable".
In December it was disclosed that one prisoner had gone on to murder his girlfriend.
The union Napo, which represents probation officers and court staff, has called for tighter checks on domestic violence offenders.
'No checks made'
It pointed out that registered sex offenders and those convicted of serious violence were not entitled to early release.
Probation staff have reported a number of cases in which domestic violence offenders were released without risk assessments or checks on their accommodation, according to Napo.
Sometimes offenders were returning to live with their victim, and were committing further assaults, it said.
Harry Fletcher, assistant general secretary of the union, said the end of custody licence scheme was "introduced quickly" and was "clearly flawed".
"Men convicted of offences of domestic violence are being let out without any accommodation check and returning to their partners' addresses," he said.
Napo had drawn up a dossier of almost 30 problem cases highlighted by its members in the past four days, he added.
"In 19 of the cases the offence involved domestic violence and the prisoner was also deemed high risk.
"In eight cases a further offence of domestic violence was alleged to have occurred during the period of licence," Mr Fletcher said.
"There is now clear evidence that further assaults are occurring and the men are either being charged with further offences or returned to prison. This is clearly unacceptable."
He said the Ministry of Justice should now review its procedures and ensure proper risk assessments were carried out.
Any necessary measures - such as a civil injunction or supervision order - could then be put in place before an offender was released, he added.
Government figures released last week showed the number of prison inmates in England and Wales had reached a record 83,181- 29 places below the "operational" maximum capacity of 83,210.
In Scotland, certain categories of prisoners can be released between 14 and 135 days early under the Home Detention Curfew (HDC) scheme.
They must wear an electronic tag and are restricted to a particular place, usually their own home, for 12 hours a day.
Before being considered for HDC, all prisoners are risk assessed. Some, such as sex offenders, cannot be considered for it.