Image copyright PA Media Image caption Three Barlinnie prisoners were found dead

Four prisoners have been found dead in Scottish jails in four days.

Three of the men died at the country's largest jail, Barlinnie, with the fourth found dead at Low Moss in Dunbartonshire.

Fatal Accident Inquiries (FAIs) will be held into each death.

It came as MSPs heard evidence on a report from the public spending watchdog which said Scotland's prison service was on the brink of a safety crisis.

The three Barlinnie prisoners found dead were Paul Hamilton, 43, who died on October 24, a man whose family have yet to be informed who was found dead three days later and Michael Charlton, 34, who died on October 28.

A fourth prisoner, Neil Hand, 30, died at Low Moss on October 27.

BBC Scotland understands at least two of the men died from natural causes - but FAIs are mandatory for any death in custody.

Hamilton was convicted at Glasgow High Court in July 2018 of attempting to pervert the course of justice and jailed for three years. It is understood he was to be released soon.

The other three men were remanded in custody and were awaiting trial.

On Thursday, Holyrood's Public Audit Committee took evidence on the Audit Scotland report which said the Scottish Prison Service (SPS) faced profound challenges in continuing to operate safely and effectively.

The Auditor General said the service's revenue budget reduced by 12.5% in real terms between 2014/15 and 2018/19, from £394.7m to £345.2m, while its costs were rising.

Prisoner numbers increased by nearly 9% in 2018/19, to 8,212, and were set to rise further, while at the same time there had been significant increases in assaults by prisoners against staff and other prisoners and in stress-related sickness among staff.

MSPs urged to visit 'shocking' Barlinnie

Caroline Gardner, Auditor General for Scotland, said: "Scotland's prisons are running well over operating capacity. The Scottish Prison Service faces a combination of severe pressures on many fronts; this poses a threat to operational safety, effectiveness and financial sustainability."

The committee heard 10 of the country's 15 jails were operating over capacity, with Barlinnie 40% overcrowded. Staff sickness levels at Perth Prison had risen to 50%, MSPs were told.

Addressing MSPs the Chief Inspector of Prisons for Scotland, Wendy Sinclair-Geiben said the increasing prison population meant it was becoming more difficult for staff to offer meaningful activities to inmates, leading to them spending more time in cells.

And she drew attention to the crumbling nature of Scotland's older jails.

"Barlinnie is shocking," she told the committee. "I urge you to go and have a look at it; to walk along corridors where plaster dust rains on your head.

"To walk around in the evening and think 'Oh my goodness' we actually see Scotland as leading edge in penology and yet we're happy to ask staff and prisoners to live and work here. I feel quite strongly, even though I recognise we are in a period of fiscal prudence."

Glasgow City Council is to consider plans by the end of 2019 for a new 1,200-capacity prison to replace Barlinnie, but the SPS said it was unlikely it could be completed before 2025.

An SPS spokesman said prisoner numbers were increasing because of a number of factors including jail sentences getting longer and long sentences being handed out, reflecting the growth in historical sex cases.