A New South Wales police officer drew his gun on a man who evaded a random breath test just inside the ACT border.

Dash-cam footage shows an officer following a car for a short period of time, before the driver pulls over and is told to exit his car at gunpoint.

The incident occurred in January 2015, but the video was only produced in the ACT Magistrates Court last week by the driver's lawyers as they fought a drink-driving charge.

The court heard the man had seen the RBT set up on the road ahead and evaded them by taking a side road.

The man's lawyer, Adrian McKenna, argued that as well as an improper use of force, the breathalyser used by the officer was not registered under ACT law, like it was just across the border in NSW.

"The magistrate decided quite clearly the breath-scanning device was not an approved device," Mr McKenna said.

"As a consequence, she decided she didn't have to make a formal finding as to whether the improper arrest justified the evidence obtained."

NSW Police are reviewing the incident.