There are now 15,000 cases backlogged, and 49% are more than one month old. In the first months to October last year, the number of cases had doubled from 7000 to 14,000.
The FDA union, which represents more than 350 members of mainly legal staff and lawyers at the Crown Office and Procurator Fiscal Service (COPFS), yesterday criticised ministers for failing to retain adequate levels of staff.
But the Crown Office denied the claims, saying it has 50 more staff than five years ago when the number of cases reported to it was at its highest. A recruitment drive is planned for next week.
The Herald reported yesterday that prosecutors are not preparing thoroughly for summary cases – those heard before a sheriff or justice of the peace – by failing to view CCTV evidence and read witness statements due to time constraints.
The Inspectorate of Prosecution highlighted major concerns and unacceptable practices in Scotland's prosecution service, resulting in excessive delays in court cases.
Jim Caldwell, Scottish secretary of the FDA, said: "This report clearly exposes the concerns over staffing levels the FDA has been highlighting for the last two years.
"Ministers cannot continue to expect staff to shore up their failure to retain adequate staffing levels in the service. The Scottish Government made it a priority to protect the current number of police officers, while the number of prosecutors has reduced.
"Without enough prosecutors and support staff the legal system will not operate effectively. Our Justice Committee evidence of October 2011 stated that the backlog of cases to be assessed by prosecutors was rising, and to date it continues to grow.
"We know COPFS management have introduced new technology and restructured the service in an effort to cope with reducing staff numbers, but at a time when we are being asked to do more and more, it is about time ministers listened [to] staff."
A number of statutory offences – including knife-carrying and most road-traffic offences – are time barred and must be dealt with within six months.
A former fiscal said staff shortages and lack of time to properly prepare cases has been a problem for some time. He said: "The inspectors identified issues inherent in summary trials procedures which existed for some years before the report."
The inspectorate report praised prosecutors and other staff. But it also highlighted lost evidence, the citing of unnecessary witnesses and incorrect requests for productions – the pieces of evidence put before the court.
It revealed fiscals "with very few exceptions" did not read full statements before court but "cherry picked" those they would read fully due to time limits.
Catherine Dyer, a Crown Agent, pointed out that when the number of cases reported to the service was at its highest in July 2007, there were 446 legal staff. In June, with a significantly reduced case load, it had 497.
She said: "It is absolutely not the case that COPFS does not have sufficient staff to deliver a modern and effective prosecution service for Scotland.
Advertisements are to be placed next week for procurator fiscal deputes as part of a commitment to front-line prosecution, she added.
Ms Dyer said: "As the FDA themselves have recognised there are peaks and troughs in our workflow and staffing created by differing circumstances."
She added that extra efficiencies would be created and a restructuring was under way to allow staff to focus on a specific category of casework and increase their expertise.
A Scottish Government spokesman said: "Operational matters in relation to the Crown Office and Procurator Fiscal Service in Scotland are matters for the Lord Advocate, who acts independently in exercising his prosecution functions."