Judges yesterday backed an appeal by a man, who claimed his rights were breached because his complaint against the former Strathclyde Police was investigated by officers at the force.
Kevin Ruddy, 33, claimed that allowing police to investigate fellow officers after his allegation of assault breached article three - the right to an effective investigation of allegations of ill treatment in police custody.
The ruling could force changes in the way that Police Scotland investigates serious complaints against officers.
Scores of people could come forward with claims for damages because similar allegations have been investigated first by officers from the same force.
The Court of Session ruling states that the obligation on the state is to provide "the appropriate independent investigation". It adds: "Where that adjectival obligation is not fulfilled, the state is in breach of its obligations under the ECHR, irrespective whether, had a proper investigation been carried out, the complaint of the party making the allegation would have been upheld in substantive terms."
The Court of Session agreed that the investigation should not have been carried out by an inspector at the former Strathclyde Police force.
The creation of the new Police Investigations and Review Commissioner in April this year offers a more robust and independent complaints handling process. However, lawyers believe it still falls short of being ECHR-compliant because some initial complaints are still handled by police officers.
Mr Ruddy's civil case for damages of £10,000 against the former force has now been referred back to the sheriff court.
Deputy Chief Constable Neil Richardson, of Police Scotland, said: "We are confident the structures and processes around complaints about the police, introduced as a result of police reform, are robust and do not require to be reviewed."