The number of prisoners locked up in Scotland's jails is expected to soar to 8500 within the next 10 years, according to official projections published yesterday.

Scotland already has one of the highest prison populations in western Europe in relation to its size and despite repeated pledges by ministers to reduce it, the numbers imprisoned has risen dramatically.

In August, The Herald revealed the population had reached a new record high with 7497 people behind bars on August 28.

The Scottish Prison Service (SPS) statistics released yesterday put the increase down to a rise in the number of remand prisoners - 1567 a day in 2006/07 compared with 1242 the previous year. They indicate that the numbers imprisoned are likely to rise to 8500, but could be as high as 9400 by 2017 depending on a range of variable factors within sentencing and bail regimes.

Predictions have been revised in the past six months following a year of record highs with the average daily prison population reaching 7183. The figures would have been even higher but for an increase in the number of prisoners released on Home Detention Curfew (HDC) which has leapt from 92 in July 2006 to the current average of 300 a day.

HDC allows low risk prisoners to be released early and monitored in their homes using electronic monitoring. Most of those tagged have to remain in their home under curfew for up to 12 hours a day. Without HDC, officials have expressed concern at where they would accommodate so many inmates.

Successive inspectorate reports have warned about the increasing problems of overcrowding and its inevitable impact on rehabilitation.

Kenny MacAskill, the Justice Secretary, said the figures painted an "alarming picture" and that action was being taken to address the problem.

He said the independent Prisons Commission had been set up to look at the issue and that the range of community penalties for minor offenders is currently under review.

"I do not believe that sending an offender to prison for a short time is the best way to deal with minor offending," he said. "Far better that they are given the opportunity to repay their community for their wrongdoing."

Projections made last year put the prison population at 8200 in 2015-16. But this year's increase has seen that revised to 8400 rising to 8500 the following year. The new projections are based on the HDC figure remaining at about 300.

In a report earlier this year, Professor Alec Spencer, former head of rehabilitation at the Scottish Prison Service, warned the prison population "could well reach 11,900 and require seven new prisons" by 2030.

"Prison should be there for only for the most serious and violent offenders and that would mean only about 3000 people being behind bars," he said. "How is it that other countries with the same culture have much lower prison populations? Why is it that crime figures have fallen or remain static and yet the prison population keeps growing? Prison serves no purpose for the majority and yet we continue to lock them up.

"If the projection continue in this manner the population in 2030 will be even higher than I predicted."