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.
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