Professor Irving called for constant assessment of sex offenders

Professor George Irving, who conducted a review of the sex offenders' register, said he was not surprised police had lost track of offenders.

He said the offenders were not under 24-hour surveillance or high security.

Professor Irving's review of the operation of the sex offenders' register recommended closer scrutiny.

Professor Irving told BBC Scotland that it should be remembered that the offenders were living in the community and, from time to time, some would go missing.

'Not complacent'

"It is a matter of concern, but we must be realistic about it - not complacent, but realistic," he said.

On Thursday, the Scottish Executive disclosed that authorities do not know the whereabouts of 24 people on the sex offenders' register in Scotland.

Police believe half of them may have gone overseas.

The executive said the 24 represented only a tiny fraction of the 3,230 people on the register.

Professor Irving, of Glasgow Caledonian University, said police had done an "excellent" job of supervising those on the register, with very few powers.