The SPS was urged by Emma Jardine, policy and public affairs manager at Howard League Scotland, to increase the transparency over access to such schemes.

Figures obtained via a freedom of information request indicated that only 43 registered sex offenders completed one eight-month rehabilitation programme between April 2020 and March 2024.

But there were 144 prisoners on the waiting list for the programme as of July this year, meaning it would take 14 years to clear at the current pace.

Another programme, Selfchange, which lasts 10 months and is offered to men convicted of general violence, intimate partner violence and sexual violence, had 384 people on the waiting list in July across every prison estate in Scotland.

Yet between April 2020 and March 2024 only 94 had finished the course.

In July, His Majesty’s Inspectorate of Prisons for Scotland (HMIPS) produced a “damning” review of prisoner progression opportunities.

Ms Jardine said: “It found that the system of moving prisoners to conditions of less security to prepare them for release was simply not working.

“The gist of what [HMIPS] said was that across the whole estate there was only a handful of people who had any idea at all how the system was supposed to work and there were so many blockages in the system, and waiting lists for offending behaviour programmes, that meant less secure parts of the estate were only half full and as a result many prisoners are being kept in prison far longer than they needed to have been.”

A Scottish Prison Service spokesman said: “Offending behaviour programmes remain a key priority and work is well under way on increasing access to these courses, which are just one of the way our staff supports those in our care.”