The administration costs for the Government's gun buyback scheme are believed to have cost nearly double the initial estimate, a report shows.

The Auditor-General's report, released today, also shows it's too difficult to tell how effective the programme was without further information on the number of prohibited firearms there are in the community

The Auditor-General announced in September last year it would report back to Parliament after it had looked at how well the scheme was implemented, given its "significant public interest".

Implementing the scheme was a "complex, challenging, and high-risk task," which police had to carry out within "tight timeframes," Controller and Auditor-General John Ryan said in the report.

"The police's provisional information, as at 13 February 2020, shows that 61,332 newly prohibited firearms had been collected and destroyed, or modified by police-approved gunsmiths so that they comply with the new requirements and remain the property of their owners."

But neither police nor any other agency knew how many prohibited firearms, magazines,
and parts were in the community when the law was changed.

"The previous regulatory regime focused on firearms owners instead of individual firearms. In part, because of this, the police do not have accurate information about how many firearms there are in the community.

"Without this information, we do not yet know how effective the scheme was."

The report found the police managed the scheme effectively, communicated well with the public, and that compensation payments did not exceed what was appropriate.

But it also found the administration costs for the scheme were more than expected.

In March last year, police produced an initial estimate of $18 million to administer the scheme.

"The estimate was based on limited information from the Australian buyback scheme and was completed quickly, before the costs of the supporting technology were fully known," Ryan said.

"The police now estimate that, once fully completed, administering the scheme will have cost up to $35 million. This includes costs of tracked staff time, contractors, and goods and services.

"This is nearly double the $18 million the 2019 Budget provided and includes about $5.5 million the police spent on the scheme in 2018/19."

The police used baseline funding from the General Crime Prevention Services appropriation to cover the excess administrative costs.

There was no evidence of "wasteful spending".

The report recommends police continue to build relationships with firearms owners and dealers, improve the information they use to keep on top of gun regulations, and create a framework to show how the new regulations have made New Zealand safer.

That included taking steps to find out the level of compliance the scheme had achieved.

In last year's Budget, more than $200 million was allocated to fund the buyback scheme.

The Government moved swiftly to ban most semi-automatic assault rifles and certain high-capacity magazines after the Christchurch mosque attacks, which claimed 51 lives.

Police held 685 collection events across New Zealand from Stewart Island to Kaitaia, and went to more than 270 private homes to collect firearms.

Forty-three gun dealers also collected 6145 firearms on behalf of police.