A gun owner says police shouldn't be in charge of firearm licenses after they mistakenly sent him an approval for a license intended for someone else, with enough information to "rob them blind of their collection".

The approval letter - which included the intended recipient's name and address - was for a special P-endorsement addition to a gun license.

The endorsement allows holders to possess or use otherwise prohibited items like pump-action shotguns with a detachable magazine, or semi-automatic firearms, magazines and parts. Under certain circumstances, it allows holders to use these weapons for pest control.

The P-endorsement was introduced last year as part of a raft of sweeping changes to New Zealand's firearm laws in the wake of the Christchurch terror attack on March 15, 2019. 

The recipient, who wishes to remain anonymous, told Newshub it's "pure luck" that the letter was sent to him and not a gang member, who may have tried to use the letter to rob the intended recipient of his weapons or access the endorsement themselves.

"I could have redirected his license to another address and used it to buy prohibited firearms, or restricted firearms," he said.

"The worst-case scenario is that the police could accidentally send private information to someone who would then misuse it to acquire the most restricted firearms you can get.

"It appears to be plain carelessness. This could have gone to anyone."

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The man believes he got the letter because he shares a similar email address to the intended recipient - not because he's a B-endorsement license holder himself. 

Police wouldn't comment on how the mistake happened, other than to say it was "human error".

"Police acknowledge that information was erroneously sent to a member of the public regarding their endorsement approval letter that only provided the name and address of the successful applicant," a spokesperson said.

"Police have spoken to the individuals involved and have apologised for this error... We are constantly working to update our processes to ensure we are following best practices."

While police say it takes incidents of this nature seriously, it told Newshub the information contained in the approval letter would not have allowed anyone to purchase prohibited firearms.

But the man says while his approach was to notify both the police and the intended recipient of the botch-up, it's feasible that he could've used the letter to access prohibited firearms if he'd wanted to.

"Right now the P-endorsement is new and dealers are showing the utmost caution and verifying everyone's identity," he said.

"But had someone acquired this license due to a police blunder and sat on it for a while, eventually an opportunity would have presented itself.

"It's clearly a case of sending incredibly sensitive private information to the wrong email address. Our emails are similar, but at the same time it's blatantly obvious to the sender at the police that the email they used is wrong."

The man told Newshub the police's Prohibited Arms Endorsement team did not respond well to him notifying them of the error.

"I don't believe they've truly accepted fault in this situation and I don't believe that any procedural improvements will arise from this," he said.

He says the mistake is proof police cannot be trusted to manage the Arms Act, and argues that its administration should instead be given to a new independent body.

"Rarely do police seem to have the time to even enforce the new laws or proactively find people illegally in possession of guns," the man said.

"It just makes sense to clear their plate and give the Arms Act administration to someone else."