HM Inspectorate of Prisons for Scotland (HMIPS) found that the prison’s infrastructure “represents a barrier to safety and acceptable living standards”.

Letham Hall, which houses inmates serving life sentences or long-term prisoners who are nearing release, was described by inspectors as being in a “wretchedly poor state”, having failed to improve on its earlier “state of disrepair”.

The report stated: “Our 2019 inspection report identified Letham Hall … as being in a state of disrepair. Five years later, despite some refurbishment, it remained in a wretchedly poor state.

“The need for a replacement prison through the planned new HMP Glasgow remains overwhelming and urgent.”

The report found that around two-thirds of prisoners were sharing cells that were intended to hold one one.

The survey also found that half of prisoners had seen staff “abusing, bullying, threatening or assaulting” another prisoner, describing this as a “serious cause for concern”.

HMIPS stated: “The need for a replacement prison through the planned new HMP Glasgow remains overwhelming and urgent. The other deeply concerning factor was the unacceptable level of overcrowding.

“Designed for single occupancy, at the time of our inspection, the prison was more than 30% above its design capacity, with almost two-thirds of prisoners having to share cells designed for one person.”

An SPS spokesperson said: “We welcome this report from HMIPS, which highlights the excellent support for first-time offenders upon arrival into custody, lifesaving Naloxone training, efforts to encourage people back into education, and the ground-breaking healthy dads, healthy kids programme, as well as some of the challenges the establishment faces.

“The Scottish Prison Service takes a zero-tolerance approach to bullying and, while we note inspectors did not witness bullying but rather found staff to be engaging and respectful to people in the care of HMP Barlinnie, we are not complacent and are committed to developing a new strategy later this year after drawing on external expertise.

“We have been managing an extremely high and complex population for more than a year, and this puts pressure on everyone living and working in our establishments.”

Justice Secretary Angela Constance said: “I recognise … the need for a replacement, which is why a contract was signed in January to build the new HMP Glasgow. It will increase prison capacity, transform how prisoners are rehabilitated, improve staff working conditions and generate up to £450m of economic benefits.”