Visiting prisons is one of the seven virtues recorded in the 15th-century carvings at Rosslyn Chapel.

It was the same Christian impetus that led to the formation in the 1870s of Scotland's first prison visiting committees. Their work, upholding prisoners' rights and opening the penal system to public scrutiny, has continued more or less unabated ever since.

Now the Scottish Government seems determined to do away with them. Why remains unclear. In 2005 a review concluded that the 16 visiting committees provided "a unique community-based means of ensuring that the people detained on our behalves in prison are decently treated, regardless of what they have done".

A second review, starting in 2010, produced overwhelming support for retaining visiting committees, including from prisoners themselves. Unsurprisingly, the main advocate of abolition is the Scottish Prison Service (SPS) because, as former Scottish Conservative leader Annabel Goldie put it in a debate at Holyrood yesterday, their work monitoring prisoners and investigating complaints is as welcome to the SPS as "a thistle in the backside".

Visiting committees illuminate the gaps between official policy and what actually happens in practice, then raise these issues with prison management and, where necessary, directly with the justice department.

Justice Secretary Kenny MacAskill says the consultation failed to produce "decisive evidence" in favour of keeping the system. That is highly questinable. Where is the decisive evidence in favour of abolition? There is none.

Scotland's prison visiting committees vary considerably in quality and effectiveness. Mr MacAskill quotes the example of Barlinnie where only 14 prisoners asked to see a committee member last year but that is not a fair reflection. Others handle hundreds of complaints and one was the subject of a visit from a Russian delegation last year, which admired the measure of public accountability it brought to the system.

Most visiting committees are appointed by local authorities, forming an important link between penal institutions and the local community. And although the prison inspectorate complements their role, it cannot replace the facility for individual committee members to make frequent unannounced visits and win the trust and confidence of inmates.

Mr MacAskill muddies the waters with his plan to set up a professional advocacy service. Many would support such a service, if the funds could be found to pay for it, but advocacy and monitoring are separate activities. There are also doubts that a company or charity, on a contract from the SPS, would be truly independent. The unpaid visiting committees certainly are.

Every government likes to promise a "bonfire of the quangos" but, in these straitened times, a good reason for retaining visiting committees is that they offer outstanding value for money at just £75,000 a year. Instead of doing away with them, the Scottish Government should be resourcing them better so that training can be improved, prisoners made more aware of their existence and best practice used to improve the general standard. Prisons may have changed since Victorian times but the same reasons to bring prison visiting committees into existence 135 years ago hold good today. Mr MacAskill must reconsider.