WITH the festive season drawing closer, police will be preparing to step up their annual drink-drive crackdown to catch out motorists over the alcohol limit.

The increased patrols, along with the public safety campaigns which accompany them, have become a fixture of the Christmas and New Year holidays. Reassuringly drink-drive deaths - in Scotland at least - appear to be on the decline.

However, as The Herald reported last month, efforts by the Scottish Government to reduce deaths further by cutting the blood-alcohol limit from 80mg to 50mg per 100ml are being hampered by delays in recalibrating breath-testing kits. This process of standardising the equipment is reserved to Westminster, but experts there have been busy honing the new drugalysers required for roadside testing of motorists driving under the influence of illegal and prescription drugs in England and Wales.

Drug-driving is a strange anomaly. While there is a long-standing criminal offence in the UK of driving while impaired due to drugs, successful prosecutions are complicated by the need to demonstrate actual impairment as opposed to simply being "over the limit" as in the case of alcohol. Even if convicted, the maximum penalty is a one-year ban and a £1000 fine.

The passing of the Crime and Courts Act 2013 in April was intended to overcome this obstacle by creating a new offence of "attempting to drive or being in charge of a motor vehicle with a specified controlled drug in the body above the level specified for that drug".

The move was welcomed by motoring and road safety groups. A poll in September indicated that one-in-five car owners had driven under the influence of drugs - mainly cannabis or prescription drugs at concentrations which might now be considered criminal - while figures from the Department of Transport suggested that drugs were a factor in 640 accidents across Britain in 2011, including 49 fatal crashes. The AA claims the death toll from drug-driving is more like 200 annually.

Drug testing is obviously more complex than breathalysing for alcohol, however. One, you have to decide which drugs to test for, and two, how to test for them. So far, the experts in Whitehall have perfected a kit which uses a mouth swab to analyse for cannabis, eliminating the need for a doctor to take a blood sample, but testers for other drugs are still in the works. A UK-wide consultation which concluded in September also sought views on how to set new drug limits - from blanket zero tolerance for all controlled drugs to linking limits to impairment.

The results of the consultation have yet to be published, but the likeliest outcome appears to be zero tolerance for illegal drugs including cannabis, ecstasy, cocaine, LSD and heroin, with limits for prescription drugs known to affect driving above a certain dose, such as temazepam, diazepam and methadone. Prosecutions of drivers caught over the legal drug limits are expected to begin as early as next year south of the Border, and those caught could face a 12-month ban, six months in jail or a maximum £5000 fine.

If successful, Scotland is expected to follow. The question is, what will we have first: drug-testing or a 50mg drink-drive limit?