The Crown Office has confirmed that at least nine G8-related protest prosecutions due to be heard in Perth have been abandoned.
A number of trials at Perth Sheriff Court this week will not go ahead despite having already incurred sizeable legal costs.
The SNP asked if the decision not to proceed could have been taken earlier.
More than 350 protesters were arrested during the G8 summit at Gleneagles in July and many later appeared in court.
Five people were due to stand trial at Perth Sheriff Court this week and four more next week, but the charges in all those cases have been dropped.
However, they have already resulted in significant costs in court time, legal aid and fees for translators.
Bringing police witnesses from forces across the UK for a trial would incur even higher costs.
The Crown Office said each case was judged on its individual merit and that the procurator fiscal would decide whether further proceedings were in the public interest.
Although unable to give exact figures, the spokesman added that the higher proportion of cases was in Edinburgh and these remained largely unaffected.
The spokesman said: "The procurator fiscal at Perth has decided to discontinue proceedings in connection with a number of cases against individuals who were reported to him following protest activity during G8.
"These cases were reported to the procurator fiscal while G8 was ongoing.
"The circumstances were such as to merit an initial appearance from custody in court and the imposition of bail conditions to prevent any possible re-offending during the G8 summit period.
"The procurator fiscal has a duty continually to review the evidence and circumstances of a case reported to him and consider whether it remains in the public interest to proceed."
The Scottish National Party said the decision to drop the cases should have been taken earlier.
SNP justice spokesman Kenny MacAskill said: "Clearly, the fiscal has to balance the public purse with the cost of a prosecution, but there have been several court appearances for what appears to be fairly minimal offences.
"If these were trivial matters, should these people have gone beyond the salutary lesson of being detained by police and spending a night in custody?
"I can't see why these people were not given a night in the cells then told not to darken our door again - it does seem like rather a waste of public funds."
Police said 358 people were arrested during the 6-8 July summit.
The biggest number of those arrested came from England, at more than 100, with 50 coming from Scotland, 35 from Germany and 30 from Belgium.
The week saw running battles on Edinburgh's Princes Street, on the streets of Stirling and Bannockburn and at the summit security fence near Auchterarder.