THIS GUY'S THE LIMIT...

Surrey Police are intent on stopping drink- and drug-driving. JOHN EVANS blows into the bag

- JOHN EVANS

It's 5pm on a September weekday in Guildford, Surrey. For an hour, members of Surrey Police's Vanguard Road Safety team have been stopping motorists to warn them about the dangers of driving under the influence of drink and drugs, when they strike 'lucky' and nab a drug-driver.

Clues? His car reeks of cannabis and there's a box of the stuff on his dashboard. The driver's saliva is found to contain illegal levels of THC, the psychoactive component of cannabis, set at two micrograms per litre of blood. In light users, THC can remain in the blood for up to seven hours, but in heavier users it's at least 24 hours. Some users constantly microdose, so the drug never leaves their system. The roadside test, which takes around eight minutes to process, can also detect cocaine (legal limit 10mg), but on this occasion there's no trace. The driver is told to get out of his car then is handcuffed and instructed to wait on the grass verge in view of passing motorists and a small crowd of onlookers.