A little-known firearms permit which allowed John Edwards to obtain the guns he used to murder his two children has been handed out to hundreds of people in the last two years.

Last month Edwards shot dead his two children at their home in West Pennant Hills in what police called a “premeditated and planned” murder.

Despite having once been the subject of an apprehended violence order, Guardian Australia reported Edwards had gained access to the handguns he used in the shooting because the New South Wales Firearms Registry had granted him a special commissioner’s permit.

The permit allowed Edwards to undertake a gun safety course at a gun club in western Sydney despite the registry having warned other clubs not to let him near firearms only months before.

Commissioner’s permits are essentially a loophole in the state’s firearms laws. They give the registry the discretion to grant firearms permits where a “legitimate reason for possession and use of a firearm exists, but the legislation does not provide a specific licence or permit and it is considered appropriate”.

They are considered rare within the firearms industry, and are generally reserved for the use of historical cannons or for visiting FBI officers.

But data obtained by Greens NSW MP David Shoebridge reveals that in the last two years the Firearms Registry granted 174 of the permits to individuals in the state, and 72 to clubs and organisations.

The majority of the licences were related to purposes which seem to fall inside the remit of the permit – for example historical cannon owners, imitation firearms collectors and minors from other states involved in sporting shooter competitions.

But the permit data also shows Edwards was not unique in being allowed to undertake firearms training without going through the standard licence application process.

In the period between the beginning of 2017 and August 2018 the firearms registry granted 28 commissioner’s permits which allowed individuals to undertake a firearm safety training course.

Shoebridge said police should not be granting “special exemptions” for gun holders.

“Why are so many people who fail the legal test for a gun being granted special access to guns with these commissioner’s permits?” he said.

“We saw how deadly the results can be of watering down our gun laws with the tragic killing of two children earlier this year by a man who had a history of domestic violence but was still given a gun.

“The community expects the police to stop potentially dangerous individuals from being given access to guns, not grant them special exemptions.

“It’s extraordinary that when we have one woman per week being killed by their former or current partner, someone who has had an AVO taken out against them can apply to get a special gun permit.”

Edwards had been refused membership from the Ku-ring-gai Pistol Club and at least one other gun club on the Hornsby Rifle Range because of disclosures he made on an application form to ­acquire a licence.

But after initially advising the clubs not to admit Edwards, the registry eventually granted him a commissioner’s permit when the 10-year period since he had been the subject of an AVO elapsed.

The permit meant Edwards was able to begin a gun training program at the St Marys Indoor Shooting Centre in western Sydney, and eventually get access to the two “powerful” handguns he used to murder his two children.

The data also shows another 36 commissioner’s permits were granted to security firm employees in the two-year period, and Shoebridge questioned why security firm employees were “exempt from rules meant to protect the community”.

“Why are we granting licenses for silencers to people whose answers to background declarations raise red flags in the system?” he said.

“We can’t let Australia go down the US path where individuals can easily acquire firearms.”