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, according to the report by the Inspectorate of Prosecution.
It also highlights lost evidence, the citing of unnecessary witnesses and failures in making the correct requests for productions – the pieces of evidence put before the court.
Last night, opposition parties said the findings were worrying given the potential impact on costs, the administration of justice and victims of crime.
More than 60,400 summary cases were dealt with in sheriff courts last year, making up 60% of all criminal business in the courts.
In a rare insight into the workings of the prosecution service, the report revealed fiscals "with very few exceptions" did not read full statements before court but "cherry picked" the ones they would read in full because of time constraints.
The main complaint from trial fiscals around the country was insufficient time to prepare for cases, the report found.
Despite an increasing reliance on CCTV evidence, fiscals had often not watched the footage in advance, "putting them at a clear disadvantage" to the defence who might have had the footage disclosed to them, it said.
"This is clearly unacceptable," the report concluded.
Good practice was recognised by the inspectorate with committed staff and hard work, often carried out under time constraints, highlighted in the report.
However, 16 recommendations for improvement have been made.
The report stated: "Phrases such as 'keeping head above water', juggling work and shuffling responsibilities were common in our visits. Loss of staff had an impact.
"Staff themselves said they felt the pressure, and preparation of cases was suffering."
In one instance, the inspectorate revealed, the criminal history of a person unrelated to a case was mistakenly disclosed to the defence. Wider concerns were raised about criminal records not being checked in time and delays in disclosing material to the defence.
Significant delays in the Crown obtaining forensic reports were also highlighted by a Glasgow sheriff.
The report follows the McInnes review of summary justice, which highlighted major concerns with delays and "churn" of cases.
While improvements have been made, there are still concerns about excessive delays, a problem traditionally blamed on defence solicitors. Some 20,000 cases a year still require a further preparation hearing.
Labour justice spokesman Lewis Macdonald said: "There are some serious issues identified in this report which are worrying.
"This must be a wake-up call to the Justice Secretary to focus on the task in hand. Delays in the justice system are costly, can risk prosecutions, and are deeply unfair to victims of crime.
"This report must not simply gather dust on the desks of Scottish ministers."
A spokesman for the Scottish Conservatives said: "There are a number of issues raised in this report which are of obvious concern. It is critical every criminal trial held in Scotland has sufficient time and resources to allow everyone to prepare. This is not something on which corners can be cut.
"However, the report also highlights areas of best practice, which should be followed, where possible, across Scotland."
Catherine Dyer, Crown Agent and Crown Office chief executive, said: "The inspectorate's report provides many helpful suggestions for further improvements to preparation of summary cases. The report highlights many more strengths than weaknesses and notes the commitment of COPFS staff in going 'the extra mile' to ensure cases are proceeding smoothly."
She added that since the cases were examined, a "comprehensive package of measures" had been introduced to further improve the handling of sum- mary cases. As part of that, Ms Dyer said a new secure website was improving the efficiency of disclosure to the defence, adding: "COPFS is the first prosecution service in the UK to provide electronic disclosure of evidence." She also said a full electronic record had been introduced for all cases.
Ms Dyer added: "We will continue to build on these improvements to ensure we are providing the best possible prosecution service for Scotland."