Tests include touching the nose and standing on one leg

The county's police have adopted new powers in addition to the usual breath test, which does not detect drugs.

The Field Impairment Tests include touching the nose, standing on one leg or walking in a straight line.

The aim is to check a driver's balance, vision, muscle control, judgement, time perception and short-term memory.

If they refuse to take the tests or perform poorly while carrying them out, they may be arrested and a blood or urine sample may be taken from them for analysis.

The tests are to be administered to drivers who are suspected of committing certain traffic offences or who have been involved in collisions.

Scientific studies

Sergeant Daryn Pearce said: "The problem of driving under the influence of drugs has been a growing one that we could not easily detect under previous legislation.

"Our officers will not hesitate to administer these tests if they have grounds to do so.

"It may appear to be something out of an American fly-on-the-wall documentary, but many of the tests have been validated though scientific studies and are designed to take dangerous drivers off the road and improve safety for others."