By STEWART PATERSON, The Herald

A political row erupted last night after figures showed that Scotland's prison population is expected to increase to almost 10,000 inmates over the next 10 years.

The current daily average of 7376 prisoners is anticipated to rise to 9600 by 2018, the Scottish Government has revealed, and the present operational limit of 8230 will be surpassed in less than three years' time if the estimates prove correct.

The predictions are even higher than last year when the 10-year projection was an increase of 1200 to 8500. That level will be overtaken in just four years, according to the government's chief statistician.

Justice Minister Kenny MacAskill said the figures were not a surprise and added that prison building would not continue to meet rising numbers, but community sentences would be used as an alternative to short term sentences.

However, opposition parties accused the government of "complacency" and "cowardice" and called for more prisons to be built.

Richard Baker, Labour's justice spokesman, said: "Today's figures show the scale of the problem but also show the paucity of the SNP's response. "Scottish prisons are on the brink of collapse, the Prison Service themselves have warned the state they're in. This is a time for decisive action, not arrogant complacency."

Bill Aitken MSP, Conservative justice spokesman, said: "Nobody denies that we have a serious problem with overcrowding in Scotland's jails. But this is where we must act calmly and rationally. The SNP Government wants to solve the problem by emptying jails. That is cowardly and it is wrong. Supply must fit demand, not the other way round. Bluntly speaking, if we need more prison space, we must have the courage to build or to find it."

The country's prison capacity is 6625 but, with doubling up in cells, the estate can safely cope with around 8000 prisoners. However, the prison estate operates at around 20% over its design capacity.

The statistics office said that a rise in the number of remand prisoners and in criminals sentenced to terms of fewer than four years has contributed to the increase to record levels this year. More than 1600 remand prisoners are held before their trial at any one time.

If measures recommended by the Prison Commission to introduce more alternatives to custody are implemented, it has been admitted the projections may need to be revised downwards in future years, however a fall in the short term is not expected.

Plans for two new jails to replace existing buildings at Greenock and Inverness are under way and one completely new facility at Addiewell Prison, which will provide for 700 inmates, is expected to open soon. The government is also due to produce a new penal policy soon.

Mr MacAskill said: "The projections out today don't tell us anything we don't already know. While crime has fallen in Scotland we continue to lock up more offenders than ever before.

"We need prisons but inherited a prison estate that was not fit for purpose. This is why we are putting in record investment of £120m in each to deliver three new prisons and a modern prison estate fit for the 21st century.

"Prison, if necessary for a long time, will always be the right punishment for those involved in serious crime and those who are a danger to our communities.

"But we cannot, and will not, build even more prisons to fill them with those for whom prison is not the right answer. This will do nothing to tackle reoffending.

"Why should so many prisoners, committing low level crime, get free bed and board courtesy of the taxpayer when they could be paying something back through the sweat of their brow on tough community sentences."

In September, Mike Ewart, chief executive of the Scottish Prison Service, told The Herald 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.