Drones have been recognised as a very real threat to Australian cities, as the use of the technology by terrorist organisations increases.

Defence contractor EPE manager Keith Mollison, who had 25 years' experience in the British Army including a stint as deputy director of intelligence, spoke at the annual Safe Cities conference about the threat of drones on Wednesday.

"Drones can inadvertently cause significant hazards to public safety," he said at the Brisbane conference.

"The spectrum of improper and illegal use of drones, even inadvertently, ranges from mischief to mayhem to protest, even acts of terror.

"They are used for many purposes – for recreation, for journalism or commerce and a lot of legal uses as well.

"Even drones used for legal purposes have the potential to cause significant disruption.

"People who not necessarily are planning to do anything illegal or bad can have unintended consequences and in an urban environment, those can be significant."

A drone was responsible for the closure of Gatwick Airport on July 3 after it was sighted flying too close to the airport and, on Tuesday evening, a light plane reported a midair collision with a drone in Adelaide's north.

Mr Mollison said illegal uses of drones also included the delivering of contraband, such as illicit drugs or explosives.

"The use of drones by terrorist organisations is spreading at an alarming rate," he said.

"There is no doubt that militants around the world are looking at options to modify drones to disperse chemical weapons of chemical agents.

"It's happening, I'm sorry."

In an effort to combat the threat of drones, EPE has supported the development of Mesmer Counter, developed by ASX-listed Department 13.

"Mesmer is not a jammer...effectively it blocks out the controller of who is using the drone and takes over controlling the drone and presents the Mesmer operator with a range of functions," Mr Mollison said.

"It could be land the device, return to where you came from or land in a designated safe area to be dealt with later."

Mesmer version 1.5 will be launched in the third quarter of 2017 and it is understood at least one Brisbane client has already invested in the software.