The probation union Napo said not enough checks were being carried out on inmates being freed up to 18 days early under the "end of custody licence" scheme.

Early release is not supposed to be available for violent offenders but Napo claimed wife beaters were slipping through the net.

Harry Fletcher, assistant general secretary of the union, said: "The scheme was introduced quickly and is clearly flawed.

"Men convicted of offences of domestic violence are being let out without any accommodation check and returning to their partners' addresses."

Napo has drawn up a dossier of nearly 30 problem cases highlighted by its members in just 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 went on: "Once again the Ministry is being urged to review its procedures. Further violent offences against women are contrary to the Government's victim strategy and are totally unacceptable."