Police don't have the money or the manpower to make culture changes recommended by an inquiry that was sparked by allegations of police rape, says the head of the police officers' union.
Five years after a commission of inquiry into police conduct concluded, a progress report says police action on improving adult sexual assault investigation is "relatively poor" despite the time police have had to act.
In 2007, the commission of inquiry recommended a raft of changes, including how police dealt with sexual assault complaints.
It followed Louise Nicholas's rape accusations against Bay of Plenty police officers in the 1980s. Two officers were jailed for raping another woman there in 1989.
Acting police commissioner Viv Rickard said police had made huge progress in some areas, but admitted there was still a lot of work to be done before 2017, when monitoring stops.
The pace of change in dealing with adult sexual assault had accelerated considerably in 2012, he said.
"While we accept that some things should be progressed more quickly, the scale of change needs to be seen against the wider environment we are operating in."
Police Association president Greg O'Connor said the report had become "something of a ritual humiliation for police".
Police were being stretched and were not being given a budget to make the recommended changes, he told Radio New Zealand.
"Government are demanding a 14 per cent decrease in crime, they're demanding an 18 per cent decrease in prosecutions, they're demanding savings from the budget of $400 million over the next four years.
"Something's got to give."
Meanwhile, Mr Rickard said more and more staff were being trained in dealing with sexual assault complaints. Police were also trying hard to increase the number of female recruits and to help them develop successful police careers.
NZN