Experts at the University of Birmingham have found a prison treatment programme for rapists and sexually motivated murderers is helping rehabilitation but needs to be improved.

Researchers at the School of Psychology were commissioned by the Home Office and the Prison Service to evaluate the Sex Offender Treatment Programme.

The programme, devised by the Prison Service, has been running in prisons in England and Wales since 1991.

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It is a 'cognitive behavioural-approach, which aims to change the way an offender thinks about his crime and victims. It now runs in 26 prisons with 1,000 men taking part each year, and is the biggest treatment programme of its kind in the world.

Professor Tony Beech, lead investigator from the University of Birmingham's Centre for Forensic and Family Psychology, said: "We are satisfied that the programme is a success in some areas. Some areas need more attention."

Researchers studied information about 112 rapists and 58 sexual murderers.

' Grievance motivated' offenders are defined by the scheme as those who commit impulsive and vengeful offences that are not sexually motivated or planned.

Research showed that they continued to blame others for their actions even after treatment, but their grievance towards women decreased significantly and their empathy towards victims improved thanks to the scheme.

'Sexually motivated' offenders are defined as those who plan and fantasise about their sexual offences beforehand and sometimes use violence to avoid detection.

Studies showed that after treatment they took more responsibility for their offences and their empathy and attitudes about rape had improved, but their stereotypical views about women and acceptance of violence against women did not change.

'Sadistically motivated' offenders are those with shallow emotions, who are fascinated by sexual violence and aroused by thoughts of death and torture. The treatment meant they became less hostile towards their victims and people in general.