The Police Investigations and Review Commissioner (PIRC) Laura Paton said that although formal performance targets were still being met, the volume of work had grown far beyond what her staff could realistically manage.

In its annual report, published yesterday, PIRC recorded a 68 per cent rise in individual complaints and a 239 per cent increase in investigations triggered by appeal rulings following changes to the law on corroboration. It also forecast a 250 per cent surge in applications from the public seeking reviews of complaint-handling, with a “significant backlog” already in place.

Ms Paton warned that the mounting pressure “risks compromising the service we provide to the public”, adding: “While my staff are working hard to preserve our quality of service, these increases in workload are simply beyond our current capacity.”

Despite handling some of Scotland’s most sensitive and complex policing cases, PIRC has just 97 staff to absorb the rising caseload.

Scottish Tory justice spokesman Liam Kerr said: “These alarming findings point to Scotland’s police watchdog being at breaking point. SNP cuts across Scotland’s justice system are beginning to bite.”

Justice Secretary Angela Constance said the Scottish government “remains committed to supporting PIRC”.