A WA Police sergeant has been fined $400 and docked three demerit points after he was caught using his mobile phone in a marked police car.

The officer, from the Mid West-Gascoyne District, will also receive “managerial guidance”, according to a police spokesperson.

A veteran truckie turned the tables on the police on Tuesday when he took a photo of the officer on his phone at a set of traffic lights in Morley.

Camera Icon A road train driver snapped a photo of a police officer texting behind the wheel. Credit: Supplied

The road train driver, who wanted to remain anonymous, said he saw the officer “texting” as he drove towards traffic lights at the intersection of Tonkin Highway and Morley Drive about 9am.

“He first caught my eye because I looked in the mirror and saw a cop car, so the natural instinct is, ‘Oh, don’t do anything wrong’,” the truckie said.

“I looked at the car again when it was right alongside me and he was driving and texting.

“I couldn’t believe my eyes, so I looked twice. You can see quite clearly that he overshot the white line and that’s only because he was texting.”

The truckie said he decided to take a photo at the traffic lights after the officer looked at him then went back to his phone.

“What’s good for the goose is good for the gander,” he said.

He said he had made the mistake of texting and driving in the past but he recognised the risks.

“I’ve been guilty of it sometimes but I think it’s very, very dangerous and the fines should be $10,000,” he said. “Not only am I a career road train operator but I’m also a very avid cyclist. I reckon one of the biggest dangers to cyclists is people texting and he overshot that white line.”

A WA Police spokesman said there were exemptions under the Road Traffic Code which allowed officers to use devices in certain situations.

However the officer did receive an infringement, indicating the mobile was not used in one of those situations.

“WA Police has a no-tolerance approach to using a mobile phone while driving,” the spokesman said. “Distraction is a main causal factor of serious and fatal crashes on our roads and we take this offence very seriously.”