Think the testing has to be a bit better than they are.
Can't have zero levels - lots of products have alcohol in them but not for consumption. This recent case about a 'positive' test for cocaine is worth reading .... Cocaine-test bus driver wins unfair dismissal case - BBC News
I know someone who drives but under the changed rules was concerned he would have to give up as he has permanent painkiller patches applied, with a Morphine based product (but apparently a lot stronger!). They don't affect his ability to drive and in fact give him the ability to remain mobile (and sane!)
FWIW, I don't think anyone should be allowed to drive when under the influence of alcohol or drugs but have to make sure the innocent are not incorrectly caught in poor testing.
Fed up with the Whingers and Moaners. PMs Turned Off. Sayonara