Distinguishing marks

The national database has been made available to all police forces and is expected to be rolled out to the Probation Service next year. A pilot is also being carried out in the Prison Service.

Previously, police and probation officers fed offenders' details into local databases, which made it difficult to track them as they moved around the UK.

The new system's launch follows the Bichard Inquiry into how two police forces failed properly to vet Soham killer Ian Huntley.

Huntley was able to get a job as a school caretaker in Cambridgeshire despite several accusations of sex-related crimes in Humberside.

The inquiry's report called for a national intelligence IT system for all police forces to share information.

'Better assessment'

Visor also contains photos of offenders, including tattoos and distinguishing marks.

The database is still being updated and could eventually contain details on 200,000 people, the Home Office said.

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Among those already on Visor are 25,000 registered sex offenders.

Chief Constable Terry Grange of the Association of Chief Police Officers recognised there were concerns over including unconvicted people on the database.

"We are acutely aware of the balance between privacy and public safety," he told BBC News.

"But there are balances set in the chain if people think we are going too far."

'Big improvement'

Harry Fletcher, assistant general secretary of the National Association of Probation Officers, said the lack of a central database for violent and sex offenders has "clearly hampered and delayed" inquiries in the past.

He said the new system would "improve matters markedly, and will lead to better risk assessment by both probation service and the police".

Mr Fletcher urged caution over the use of sensitive information stored on the system, but dismissed fears over holding information on people who have not yet been convicted.

"Information has always been held on the police national computer about individuals who are thought to pose a risk," he said.

Shaun Kelly, a child protection manager with children's charity NCH, broadly welcomed the proposals.

He said: "In itself it's not the only thing that we need to do to reduce the risk of sex offences against children, but it is a very important process that needs to be put in place."