Roadside drug-testing will begin in March.

The Transport Department has confirmed that Gardaí are being equipped with a portable device to carry out random checks on motorists for cannabis, cocaine and heroin.

They will also test for prescription drugs.

Motorists found to have levels above legal limits will be taken to a garda station and have to provide a blood sample. Penalties for refusal to comply include a fine of up to €5,000 and six months’ in jail.

However, drivers are being reassured that they will not be penalised if they are taking medicines under the direction of a doctor or pharmacist.

The AA’s Conor Faughnan expects there to be legal challenges to the tests:

“It’s a necessary part of legislating in this country – put it all out there and make sure you think it’s tight enough. (Then,) when it gets challenged and you have your ruling from the Supreme Court, you then have a bullet-proof law that can last,” he said.