More than 3700 allegations faulting police conduct were made last year, of which more than 400 became upheld complaints.
A police conduct report has shown service failure and unprofessional attitude/language were the most upheld type of complaint last year.
The report also recorded how many allegations were made relating to suicide attempts occurring while in custody, breaches of confidentiality and misuse of a police database.
Last year's police professional conduct statistics tally all allegations made during that time against the organisation and its staff. Those allegations can be recorded in more than one category when considered by type.
Investigations are still ongoing in some cases.
Four hundred and forty-three allegations were made about inadequate service and, after 379 completed investigations, 58 complaints were upheld.
A total of 488 allegations fell into the investigation failure category and, of the 417 completed investigations, 38 complaints were upheld.
Police Association president Chris Cahill said this was a concern but not a surprise.
"What they both point to is the demand for police services outstretches the ability to provide that service," Cahill said.
There simply had not been enough resources, he said.
"There will always be some complaints that simply will not meet the priority and that will annoy the person who is individually affected by it."
The Government recognised the insufficient resourcing with 1800 new police and 485 non-sworn police employees and in turn expected an improvement in service, he said.
According to the conduct report 478 allegations were made externally about unprofessional attitude/language and, of the 404 completed investigations, 56 complaints were upheld.
However, Cahill said this was a low figure considering the thousands of interactions police had with the public daily.
"Police officers are human, they get frustrated and reacted badly sometimes," he said.
"The people we deal with aren't always the most friendly and obliging."
The report also showed that 58 allegations were made regarding attempted suicides occurring in custodial care.
Of the 38 completed investigations, 12 of those complaints were upheld.
Cahill said it signalled how many people with mental health issues police were dealing with daily and how many ended up in police cells.
Those cases were notified to the Independent Police Conduct Authority and that was where most of those complaints came from, he said.
Upheld complaints usually were because of a missed step on a checklist, he said.
"It is nearly always simply because of the workload in those custody units.
"Police stations are not the best place for someone to be kept in custody, certainly not when they have mental health issues."
Sometimes there were delays sourcing a causal jailer if one was required for constant supervision, and another staff member would be pulled away from other duties, he said.
Working in custody units was an incredibly difficult and risky role, he said.
Everyone had to try to maintain 100 per cent vigilance, he said.
"There is plenty that can go wrong."
Last year 132 allegations were made about breaches of privacy/confidentiality and, of 92 completed investigations, 21 complaints were upheld - numbers Cahill called disappointing.
Most of those allegations would relate to use of the National Intelligence Application (NIA) and Police College was spending a lot of time emphasising to recruits where the obligations were, Cahill said.
"It's something that needs to improve."
Random checks were being done as well as regular audits to check usage, he said.
Nearly all of the completed investigations about disgraceful behaviour while off-duty resulted in upheld complaints, 18 of 20, with only four investigations ongoing.
"Whenever an officer commits an offence off-duty they are charged with the offence," Cahill said.
"But the conviction rate is very low. In other words, police are quick to charge but the evidence when tested in court doesn't actually uphold the complaint."
Those numbers possibly reflected admitted lower-level offending, he said.
"We have a lot of young police officers, who are new to the role, they go out and socialise with people who aren't police officers.
"Sometimes you just step over the line a bit."
A warning was appropriate in those cases, he said.
"Learn from your mistakes. You have to remember when you join the police you set higher standards for yourself."
Seventy-four allegations were made about a conflict of interest and, of the 55 investigations completed, 13 complaints were upheld.
"It's a little bit a reflection of how small New Zealand is," Cahill said.
Responses in smaller communities could technically pose a conflict but they are trying to resolve the immediate conflict, he said.
WHERE TO GET HELP:
If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call 111.
If you need to talk to someone, the following free helplines operate 24/7:
DEPRESSION HELPLINE: 0800 111 757
LIFELINE: 0800 543 354
NEED TO TALK? Call or text 1737
SAMARITANS: 0800 726 666
YOUTHLINE: 0800 376 633 or text 234
There are lots of places to get support.
For others, visit: https://www.mentalhealth.org.nz/get-help/in-crisis/helplines/
There were 36 allegations made about unauthorised use of a database and of the 16 investigations completed half of those complaints were upheld.