Drug-driving in England, Scotland and Wales

[Paul]

Pity you took an over the counter decongestant where there are no listed side effects, got stopped for speeding, tested and it still sets off the alarm bells.
False positives are common. More common than is admitted by TPTB.

So now you're arrested on the spot.
Back to the police station, photographed, finger printed and your DNA taken.
You may own a shotgun. Woops, no you don't.
Police came round and took it (just in case).
You go to court to be found innocent. Is that an end to it?
No. Apart from the fact you are now in the system, your job may have gone as your boss fired you to keep his insurance rates low.

Condemn away by all means but it could be you for no more reason than an a simple allergy and a false positive result.