A motorist has made use of a little known rule, to successfully wriggle out of a speeding fine

Alex Mercer sped up to avoid colliding with a slower driver, when the driver he was passing unexpectedly sped up.

A High Court judge agreed Mercer exceeded the speed limit so as to avoid death or injury.

Former police officer Hamish Piercy says there's a clause in the law which allows it, on a case by case basis.