The figure for October last year was 7,835, and figures from Scotland's chief statistician showed it was projected to be 8,100 for 2009-10. The number of criminals is then expected to carry on rising – with the total projected to reach 9,000 in 2013-14 and increasing further to 9,600 by 2018-19.
The report, released yesterday, said the prison population had been at "record" levels in 2008 and 2009. It added the main reason was the increasing number of offenders given jail terms under four years. The number of these short sentences has "increased steadily" since 2007, reaching about 3,500.
Justice secretary Kenny MacAskill said: "These projections confirm what we already suspected: that if current trends continue, Scotland will continue to lock up more and more of its people, many for very short periods. This is despite recorded crime being at its lowest level for 30 years."
Mr MacAskill has set out proposals to reduce the number of criminals sent to jail for periods of six months or less, arguing these people should instead be given tougher community punishments. He said: "Serious criminals deserve to go to jail, but they find themselves in prison alongside too many individuals who, quite frankly, would be better dealt with through tough community payback – clearing snow and ice, repairing paths or landscaping parks and gardens."
However, Labour justice spokesman Richard Baker accused Mr MacAskill of "losing control" of the prisons issue and said his only strategy was scrapping six-month sentences. "Today's figures show the scale of the problem, but also show the paucity of the SNP's response. The SNP's only strategy so far is to see them want to scrap six-month sentences that would see thousands of knife criminals, muggers and housebreakers dodge jail entirely."
He added: "Since the SNP came into power almost three years ago, not one new establishment has been fully commissioned, and the future plans for the service include replacing Greenock and Inverness prisons without increasing capacity."
Tory justice spokesman Bill Aitken said: "That the prison population is likely to soar is a most worrying situation, but Kenny MacAskill seems to be blind to the consequences of his actions. He has to strike a balance between the safety and security of the public and supplying an adequate number of prison places. Simply letting people out after serving a fraction of their sentence does not work."
But John Scott, chairman of the Howard League for Penal Reform in Scotland, backed Mr MacAskill's proposals. He said: "The prison estate is already significantly overcrowded. Short term sentences do no good in terms of the loss of contact with families, jobs and housing.
"I hope there will be fresh impetus from the political parties who oppose scrapping short term sentences to readdress the issue as a matter of urgency."