Prison staff in Scotland are opting to quit after taking sickness absence because the thought of returning to the environment is too much for them to take, MSPs have been told.

Overcrowding in prisons combined with increases in violence, mental health issues and the use of psychoactive substances have all been raised as key factors in staff choosing not to return after taking time off.

Wendy Sinclair-Gieben, HM Chief Inspector of Prisons for Scotland, said: "In my experience, and as I've done all the inspections and spoken to staff and to prisoners, the two items that come out most strongly is their concern about whether they're dealing with mental health correctly – whether they've actually got the right approach.

"And the second one that comes out is the psychoactive substances, and I think it's important to remember that psychoactive substances are relatively new."

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Phil Fairlie, Scottish national chairman of the Prison Officers Association Scotland, made the comments to Holyrood's Audit Committee on Thursday as it heard evidence from prison bosses.

It follows a report from the Auditor General which highlighted a "significant" increase in assaults by prisoners against staff, while stress-related sickness among workers had risen by nearly a third in 2018/19.

The National: Scottish prisons are seeing an increase in drug consumption and mental health issuesScottish prisons are seeing an increase in drug consumption and mental health issues

Fairlie said: "I think the sick absence in Scotland, some of that's to do with the change in the environment.

"The overcrowding, the increase in the violence, the psychoactive substances and the impact it's having on the regime, is actually a fairly new and recent thing.

"And I think that's had an impact on staff awareness of how to deal with that environment and how to cope in that environment.

"I think it's left a much more unsettled staff group than we've had for quite considerable time.

"We've got very stable, organised prisons and I think what we're getting at the moment is they're still stable, well run, organised prisons, but there's less certainty amongst the staff about what it is they're dealing with.

"Some of the types of violence, some of the mental health issues that they're dealing with, the growth in the mental health issues we're dealing with, is a real challenge for some of the staff and some of them are struggling to cope with that."

Fairlie said the prison staff population in Scotland differs from that in England as it has an older age profile, with a higher number of "mature, longer-serving" staff, as opposed to south of the border where more staff are in the earlier years of their careers.

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He said the increase in the retirement age for staff is pushing many to choose to quit, rather than return to work for the remaining years of their working life.

"When they go sick in their 40s and 50s, in terms of the retirement age having now disappeared into the horizon for a lot of the staff, the thought to come back is a much more difficult one to make, and actually a lot of the staff that are off sick just now will not return to the staff, they won't come back," said Fairlie.

"We've got an awful lot of staff who the thought of coming back is just too much for them."