By Jenness Mitchell and Alison McCallum

The Scottish Prison Service is facing profound challenges in continuing to run the country's overcrowded jails safely and effectively, a public body has warned.

A report by Audit Scotland revealed that the service's reduced budget, increased prisoner numbers and rising stress-related staff sickness "poses a threat to operational safety".

Instead of "throwing money" at the issue, Scotland's justice minister Humza Yousaf believes combative measures will have to be 'bold, radical and controversial at times' to reduce the prison population.

Audit Scotland's report highlighted that the service's revenue budget declined by 12.5% in real terms between 2014/15 and 2018/19, from £394.7m to £345.2m, despite its costs rising.

Prisoner numbers increased by nearly 9% in 2018/19, to 8212, and are set to rise further.

Financial pressures are also "compromising efforts to prepare and support prisoners for life outside prison".

Over the last two years, there have been significant increases in assaults by prisoners against staff and other prisoners.

Stress-related sickness among staff also rose by nearly one third in 2018/19, and additional payments to staff working longer hours increased by 65% to £4.25m.

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."

Just last month, the chief inspector of prisons said she was "very concerned" that the number of inmates in Scotland was starting to exceed capacity, placing extra pressure on the system.

Wendy Sinclair-Gieben, HM Chief Inspector of Prisons for Scotland, said the 9% increase is equivalent to one additional large prison.

In her report for 2018/19, she said planned investment in key infrastructure should not be delayed and called for urgent action to replace HMPs Barlinnie, Greenock and Inverness, saying Victorian prisons are "costly and no longer fit-for-purpose".

She said: "The additional number of prisoners and an increasingly complex population places a heavy burden on an already overstretched prison service in Scotland.

"I am very concerned that the number of prisoners is starting to exceed design capacity, resulting in not only additional pressures on staff, the prison regime and activities, but also on the essential programme and through care activities designed to reduce recidivism."

Scotland's incarceration rate is one of the highest in Europe, while the number of prisoners on remand awaiting trial had risen from 1142 last year to 1350 by March 31 this year.

Justice secretary Humza Yousaf told STV News that he didn't want to get into the "habit of building more prisons".

He said: "Actually, if you look at the auditor general's report - all of the issues that they highlight, the root cause of them is that we have far too many people in our prisons.

"We have the highest prison population in Western Europe. That puts pressure on prisons, that puts pressures on the estate, puts pressure on staff.

"So of course the funding issue we will look at - and will look at and consider carefully - but actually if you want to tackle the root problem, we have to reduce the number of prisoners in our prisons.

"So that is what I will be working towards - in terms of bringing progressive justice reforms to this parliament - and hope the rest of parliament will get behind that initiative so that hopefully we can address some of these root problems.

"The root of this, as I keep saying, is that we have far too many prisoners in our prisons.

"If we reduce that number through community alternatives, reduce that number through bail supervision and other measures, then actually we can spend more time working on the rehabilitation of prisoners so that they don't come back in that revolving door.

"So, there's a lot more we can do, but it's only going to happen if we manage to reduce prisoner numbers."

The justice secretary said he would look at the funding concerns, but stated that "throwing money" at the issue was not the solution.

He instead believes combative measures will have to be "bold, they're going to have to be quite radical, and frankly a little bit controversial at times in order to reduce our prison population".

In response to Audit Scotland's report, Scottish Conservative shadow justice secretary Liam Kerr said: "This lays bare just how badly the SNP government has mishandled the prisons system over more than a decade.

"Ministers' failure to plan properly has led to a crisis in finances, prisoners not being rehabilitated properly and an increase in assaults.

"The SNP might shrug its shoulders and say prisons are overcrowded, and therefore a soft-touch agenda must be enacted.

"That's not good enough. The SNP's failure to provide sufficient jail capacity should not lead to Scotland's communities being flooded with dangerous criminals who've been released early, or dodged prison altogether."