Assistant Commissioner Phil Wilkinson said the Police Commissioner's exemption to firearms regulations, which allowed dealers to accept unregistered firearms without risk of prosecution, had been found invalid by the police's own legal team.

The exemption, in place since 1997, inoculated dealers from charges of receiving or possessing an unregistered firearm and allowed them to register those firearms on behalf of the owner or for sale.

Now that exemption has been rescinded, dealers must join unregistered gun owners in approaching police for help to register or get rid of an unregistered firearm, or face criminal charges. Police will not charge anyone for firearms received while the exemption was still in place.

Mr Wilkinson said the issue was raised for the first time with police by a dealer in November and was not connected to the review of the Firearms Act, which is still under way.

"Everybody has been acting under the belief - that's us and the firearms dealers - that it was a valid exemption," Mr Wilkinson said.

"Once it was brought to our attention we made some inquiries ... we took some advice and it was indicated that the exemption was beyond the Commissioner's powers."

Anyone with an unregistered firearm may hand it in to police at any time and not be penalised.