The prison service is struggling to maintain order in Scotland's jails because of record numbers of inmates, its head has told MSPs. Mike Ewart, chief executive of the Scottish Prison Service, has written to MSPs outlining the scale of pressure, risk of disorder and concerns for guards' safety.

The prison service is struggling to maintain order in Scotland's jails because of record numbers of inmates, its head has told MSPs.

Mike Ewart, chief executive of the Scottish Prison Service, has written to MSPs outlining the scale of pressure, risk of disorder and concerns for guards' safety.

He warned: "Scottish Prison Service can no longer guarantee that the continued operation of Scotland's prisons is operationally safe or compliant with our legal obligations."

The letter comes after The Herald revealed Mr Ewart's concerns earlier this month that Scotland's prisons were in a state of emergency and were a risk to inmates, staff and the country. He called for a cap on numbers to help cope with overcrowding, which reached unprecedented levels last month.

The country's prison capacity is 6625 but, with doubling up in cells, the estate can safely cope with an estimated 8000 prisoners.

The prison estate continually operates at around 20% over its design capacity - and hit a record 8137 on September 15.

Barlinnie jail coped with a 73% level of overcrowding last week - holding 1764 prisoners in a building fit for 1018 and in excess of the building's safe limit of 1600 prisoners.

Mr Ewart set out his case to the Scottish Parliament's justice committee, which meets on Tuesday.

He said the budget awarded to the prison service last year was "satisfactory" for the projected prisoner population of 7500 with an additional 300 on home detention curfew.

But he added: "September population levels have already reached the level projected for 2013/14 - some five years earlier than predicted.

"Inevitably, this unplanned increase in the prisoner population has placed unprecedented pressure on the prison system and, in particular, the staff and resources available to the Scottish Prison Service."

Labour justice spokesman Richard Baker said he had asked for an urgent meeting with Mr Ewart "and will also visit Barlinnie Prison to see for myself what's going on".

Mr Ewart's stance has been backed by Dr Andrew McLellan, Her Majesty's Chief Inspector of Prisons, who said overcrowding had been causing "terrible damage" in Scotland's prisons.

The revelations in The Herald also sparked a political storm after it emerged that the Scottish Government has temporarily transferred £10m out of the prison service budget into housing, with Labour claiming the move was a "damning indictment" of the handling of the overcrowding crisis.

Last week, a benefits cheat avoid jail after a sheriff told him there was no room in Scotland's overcrowded prisons. Sheriff Lindsay Foulis ordered George Munce to carry out 240 hours community service after he admitted fraudulently obtaining almost £10,000 in income support.