Three New South Wales police officers face a corruption inquiry and possible criminal charges after claiming to have been attacked by an Aboriginal man - whereas in fact he was assaulted by them.

When the case against Corey Barker, 21, came to court, police claimed that surveillance footage of the incident at Ballina police station, on the NSW north coast, was damaged. However, the tape was repaired by prosecutors, and it showed officers kicking, punching and kneeing Barker, 21, who had been arrested that day.

The officers - who last week remained on duty - claimed it was Barker who punched Senior Constable David Hill in the face. The magistrate, David Heilpern, who dismissed the charge in the Ballina Local Court this year, ruled during a legal costs hearing last week that the officers had colluded to give "palpably false evidence".

He referred his findings to the state's corruption watchdog, the Police Integrity Commission, and said he was considering referring Hill and two other officers to the NSW Supreme Court on contempt charges. The public had the right to feel confident that the police service had zero tolerance of "thugs in uniform", Heilpern observed.

He noted that the officers stuck to their story even when it was demolished by the security tape.

"It was as though there were two parallel universes in court: the imaginary one of Senior Constable Hill, and the real one that the rest of us ... could see."

According to the Ballina Advocate, Barker was arrested after interceding in an altercation between two friends in the city centre last year. Officers claimed he threw a plastic bottle in their direction, and also resisted arrest. Back at the police station, they claimed, he punched Hill in the nose after officers tried to move him between cells.

The tape showed that no such incident occurred. Instead, five officers grabbed Barker, rammed his head against the wall and then forced him to the ground, where Senior Constable Ryan Eckersley kicked him in the head. Another officer kneed him in the side, and he was also punched and had his hand stomped on.

He was then dragged to a cell, where he was left handcuffed for more than an hour.

Heilpern found that Hill had colluded with another officer, who then lied on oath. Awarding costs of nearly A$31,000 ($39,600) to Barker's solicitor, he said: "The court cannot stand by and allow the administration of justice to be debased by the in-court conduct of police officers giving palpably false evidence in such a contemptuous manner."

By Kathy Marks Email Kathy