The High Court ruled on Thursday that the existing mechanism to handle police complaints is in breach of the Bill of Rights on torture and cruel treatment.
It said under an article of the Bill of Rights, which bans torture and cruel, inhuman or degrading treatment, the government has a duty to maintain an independent mechanism on police complaints.
Judge Anderson Chow was responding to a judicial review application from the Hong Kong Journalists Association, which argued that the government has a duty to establish a mechanism capable of effectively and independently investigating complaints against the force.
Chow agreed with the association that the existing complaints mechanism, involving the force's Complaints Against Police Office (Capo) and the Independent Police Complaints Council (IPCC), are inadequate to fulfil the duty under the bill.
"Capo cannot, in my view, be regarded as practically independent of the force," the judge remarked, saying it comprises career officers who would return to serve in other departments of the force after working a few years at the complaints section.
Chow also said the IPCC lacks the necessary investigative powers of its own, and that it cannot overturn Capo decisions.
He noted that the council may make public its disagreement with Capo on cases and notify the Chief Executive, but "it has ultimately no power to make any binding determination".
"In all, the two-tier mechanism for handling [police] complaints... fails to meet the requirement of independent investigation [under the Bill of Rights]," the judge wrote.
Any independent investigation, he added, should be capable of identifying police officers suspected of using unreasonable force or other forms of ill-treatment.
Police said they noted the court's ruling and would study the judgement with the Department of Justice. A spokesman said the force would conduct reviews and take suitable follow-up action.
The Journalists Association also sought a court ruling on whether the government has a duty to facilitate journalistic activities in the wake of the anti-government protests that erupted in June last year, and whether it has failed to observe such duty. The judge said it will hand down a separate judgement on the matter later.