Appearing before Holyrood’s Criminal Justice Committee yesterday, Chief Inspector of Prisons for Scotland Sara Snell said the prison estate was failing to meet the UN’s Nelson Mandela Rules, which set minimum standards for the treatment of prisoners.

Asked by SNP MSP David Linden whether Scotland was at risk of breaching the rules, Ms Snell replied: “I’m afraid you aren’t at risk, you are (breaching the rules).”

She said inspections had found convicted prisoners sharing cells with remand prisoners despite a requirement to keep them separate.

“In that report we find, and we’re still finding, for example, convicted prisoners who are sharing cells with remand prisoners, when there’s an absolute requirement to keep people separate,” she said.

Ms Snell also highlighted pressures on prisoners’ daily routines, saying some were being forced to choose between activities such as exercise, collecting medication and finishing meals because of limited time and resources.

“One of the things we would point to always is just people sharing cell space that was designed barely for one and now there’s two men,” she added.

The prison population recently stood at 8,515, above the estate’s operating capacity of 8,007.

Describing overcrowding as the most significant challenge facing the prison service, Ms Snell said some institutions could feel like “one big segregation unit”.