Canada is frantically training police officers to spot drug-impaired drivers ahead of the legalisation of recreational marijuana next week.

The Canadian Association of Chiefs of Police estimated that the country would need 2,000 officers capable of testing motorists.

At the last count, only 833 have been given the necessary Drug Recognition Expert (DRE) training to enforce new motoring offences brought in to coincide with cannabis legalisation.

Any police officer is capable of carrying out roadside tests to indicate whether a driver might be impaired. In Canada, they are known as Standardised Field Sobriety Tests (SFSTs).

Similar to the Field Impairment (or FIT) tests in Britain, they require the motorists to perform such actions as standing on one leg.

However, DRE trained officers are needed to go through the more rigorous testing required under Canadian law, including taking urine and saliva samples.

The offences are for drivers who have consumed cannabis within two hours of getting behind the wheel.

Motorists with low levels of tetrahydrocannabinol - the active ingredient of cannabis also known as THC - can be fined up to 1000 Canadian dollars (£589).

Higher levels of THC or taking cannabis and alcohol at the same time can lead to a jail term or up to 10 years in the most serious cases.