Police have been accused of a "scandalous delay" of more than three years in investigating the case of a Wellington man who suffered a broken neck when police raided a party.

Wellington police say it will be another six weeks or so before they issue their findings over an incident involving Jakob Christie, who suffered a fractured vertebra when police closed down a party in Homebush Rd, Khandallah, in September 2009.

Police "had committed a serious crime and have tried for years to cover it up", says Wellington public relations consultant Iain Morrison, whose son was a host at the party.

He believes there is a "culture of lies" among the police.

A lawyer assisting Mr Morrison, Keith Jefferies, said the delay was "a constitutional outrage". "It's indicative of a police force that doesn't want to face up to its responsibilities or is just completely dysfunctional - one of the two."

Mr Morrison, who made a formal complaint to the Independent Police Conduct Authority and has kept a detailed log of the case, said "the police are thumbing their nose at their watchdog because they don't fear it".

He has called for the authority to be given the power to arrest police officers. If the authority had more power, police would be much less likely to delay and fudge their own inquiry, he said.

The young people at the party - the children of lawyers, professors, accountants and other professionals - had been "smacked around" by an out-of-control squad of police.

"I'm not anti-police," Mr Morrison said. "I have a daughter and a son-in-law in the police in Sydney."

But his experience in this case had left him cynical.

One detective who had been called in to the inquiry six months ago had told Mr Morrison that police had "stuffed up" and "hadn't done an investigation".

Wellington district police commander Mike Rusbatch said the police inquiry was finished and was now being reviewed, which would take about six more weeks.

The length of time elapsed was "not ideal", but there were "challenging aspects" to the case.

"Some of the partygoers did not want to engage in the process and despite numerous attempts to advance interviews, some did not give an account to police."

Mr Morrison said some of the young people at the party were reluctant to speak to police, which was hardly surprising. Police had beaten innocent young people in a private home, he said.

The recently appointed head of the IPCA, Sir David Carruthers, said he had still not decided whether to support new powers of arrest and prosecution for the authority.

The authority finished its work into the Jakob Christie case "some time ago", according to a spokeswoman, and was waiting for police to finish their inquiry.

Mr Christie, then 19, was found to have a fractured vertebra when he went to hospital the day after the party. He spent the next three months in a neck brace.

- © Fairfax NZ News