JAKOB CHRISTIE: Said his neck was broken by a police baton.

Police have defended their investigation into the unlawful breakup of Wellington party, saying "there was no coverup".

Responding to a damning Independent Police Conduct Authority report, Assistant Commissioner Gran Nicholls said while police had misinterpreted the law they had acted in "good faith".

He also refused to confirm whether police would apologise to Jakob Christie, whose neck was broken while police broke up the Khandallah party in September 2009.

"The issue of an apology is something that we are going to explore with Mr Christie," he said.

"It is something we need to do in a private context." Despite breaking the law by entering the house, Nicholls said none of the 11 officers involved had been, or would be, disciplined.

"Our belief is the police acted in good faith in terms of entering the property."

A previous police investigation, which took three years and largely cleared the officers of wrongdoing, had been poorly resourced but rejected the IPCA report's suggestion that it was not conducted in a "unbiased" way.

"There is no coverup."

The IPCA report, released this morning, said police had used "unnecessary, excessive force" in their handling at the rowdy party.

They were called to the party in Homebush Rd, Khandallah, in September 2009.

They arrested several people at the address, but soon after faced accusations of excessive force.

Police Minister Anne Tolley today said she was satisfied police had learned from their mistakes.

Police had "fronted-up" and we working on fixing problems raised by the IPCA, she said.

"I'm a satisfied that the appropriate changes will be made."

Christie, then 19, said a police officer struck him in the neck with a baton as he left the party, while two other partygoers said they saw a policeman beat him around the neck.

But a police internal review - released in December last year more than three years after the incident - found no fault on the part of the officers.

Eleven complaints were made to police after several young people also said they were struck with batons when the squad of 20 police officers closed down the party.

The review dismissed police culpability in each case, either because of insufficient evidence or because the force used was deemed "reasonable".

Authority chairman Judge Sir David Carruthers said the police's failure to conduct a robust, thorough and timely investigation was "unjustified, unreasonable and unfair".

"Not only have the complainants waited over three years for an outcome, the officers involved have also had this matter outstanding for the same amount of time ... such a delay is inexcusable."

Police had acted unlawfully in entering the property without permission and public order policing needed to be looked at urgently as a result, he said.

Although some of the force used was reasonable as it was used in self-defence, other force was used to unlawfully remove partygoers from the house and therefore unjustified.

The report found the baton strike on Mr Christie that broke his neck was "excessive and contrary to law".

However, the authority was unable to determine which officer was responsible.

The authority had also investigated a complaint that unauthorised material was sent to a media outlet after the incident.

The release had been made to discredit a complainant, but the administrator who leaked the information had left the police, Judge Carruthers said.

Tolley declined to comment of whether the police officers involved should be charged but said "everyone is very dissatisfied" with the police worker who leaked a report to the media in an attempt to discredit Christie.

That staff member has since left the police.