Not enough is being done by Scotland's local authorities in assessing the risk posed by serious violent offenders in their care, a four-year study has concluded.

The inspection of criminal justice social work services across all 32 councils examined the quality of reports prepared for courts and the Parole Board, and the standard of supervision of offenders on probation, parole and non-parole licence and community service.

It found more than 60% of social inquiry reports prepared were beneath a "wholly acceptable standard". In Aberdeen, only 10% of the sample was considered wholly acceptable.

The documents, compiled by social workers, help guide sheriffs and judges on what sentences to hand down to those convicted.

Social Work Inspection Agency (SWIA) inspectors found the risk analysis contained in social inquiry reports on serious violent offenders was "poor" and "uneven".

One-quarter of offenders under statutory charge of local authorities had no supervision plan. Only half of those who did had the reports routinely reviewed or updated.

They also found work with sex offenders was of a higher standard than any other group of criminals; the full potential for community service orders was not being realised; and practitioners were better at dealing with personal and social problems than the offending behaviour.

The agency makes 11 recommendations it believes will help to create more Scotland-wide consistency in performance across the range of social work with offenders.

It said: "These findings point to the need for improvements in the supervision and management of high-risk offenders, particularly serious violent offenders. The Scottish Government, community justice authorities and local authorities should give more priority to improving services for serious violent offenders."

Alexis Jay, SWIA chief inspector, will launch the findings at the Association of Directors of Social Workers Criminal Justice conference today. She said: "Since the beginning of the inspection programme there has been an improvement in performances, but there remains too wide a variation in performance across the country."

A Cosla spokesman said: "Across Scotland, we're seeing a national policy shift from prisons to community-based sentences where appropriate. This report highlights that strategy, resourcing, infrastructure and provision need to support that change if criminal justice social work services aren't to burst at the seams."