Europe’s anti-torture watchdog has described conditions in Scotland’s overcrowded prisons as an emergency situation, in a damning report that highlights a rise in drug-related violence, the overuse of segregation, and inmates confined to their cells for lengthy periods of time, sometimes in less than 3m2 of living space.

Julia Kozma, who led the delegation of the Council of Europe’s Committee for the Prevention of Torture (CPT) when they visited five Scottish prisons last October, described witnessing an influx of new arrivals at HMP Grampian. She said it was “like an emergency situation” as staff searched frantically for spare mattresses.

“We don’t see the numbers going down so the emergency is becoming more and more the norm,” she added.

However, Kozma told the Guardian it was difficult to blame the authorities when she believed the problem of prison overcrowding in Scotland, which has the second highest imprisonment rate in western Europe, was rooted in the attitudes of the judiciary.

The report reserves its greatest criticisms for the treatment of inmates at the Cornton Vale women’s prison, where the delegation found “women who clearly were in need of urgent care and treatment in a psychiatric facility, and [who] should not have been in a prison environment”.

They included one woman who had bitten through the skin and muscle of her arm down to the bone and another who set fire to her hair in her cell. Since the delegation’s visit it is understood these women have been transferred to a medium secure psychiatric facility.

While the committee heard no complaints of deliberate ill-treatment by prison staff, the long-term effects of overcrowding alongside very little out-of-cell activity – often limited because of staff shortages – had a significant impact on prisoners. In Grampian prison, the CPT delegation found mattresses had been put on the floor under bunk beds to accommodate three people in double-occupancy cells.

The report notes the rise of inter-prisoner and inmate-on-staff violence, which it links to “large amounts of synthetic drugs flowing into Scottish prisons”, often soaked into letters which prisoners then smoke. It also described an “intractable” issue of many prisoners being segregated from the main prison population for long periods of time, months and sometimes years, with some becoming institutionalised in segregation “despite living in virtual solitary confinement”.

The Scottish Prison Service said the women’s estate in particular was at an advanced stage of reform, with Cornton Vale set for closure and new community custody units under construction across the country. It said the reduction of mental health services meant women with such issues were often criminalised instead.

The SPS added that it was trialling new scanners to detect synthetic drugs entering prisons, and linked the rise in violence to an increase in the number of inmates involved in organised crime.

The CPT report notes the Scottish government has embarked on an agenda of reform, especially regarding female prisoners and young offenders, but also observes that these reforms are still at a “nascent” stage.

The Scottish government said it would carefully consider the committee’s findings. “We want to ensure Scotland is a modern, inclusive nation that protects, respects and realises internationally recognised human rights. We actively engage with international human rights monitoring mechanisms and value the expert insight they provide on human rights issues.”

Humza Yousaf, the Scottish justice secretary, has previously said the rise in the prison population was partly because police and prosecutors had placed a greater focus on serious organised crime and sexual offences.

Ministers have recently introduced a presumption against putting offenders in prison for sentences of less than 12 months, in an attempt to reduce overcrowding, but Kozmo said she believed the Scottish government accepted this would have minimal effect.

“It is difficult to blame the authorities when the issue is rooted in the judicial system that hands down long harsh sentences and is unwilling to look at alternatives. If we want to see an alleviation in overcrowding it has to include the judiciary looking at sentencing policy.”