Re: Presumption of innocence
The concept of the "presumption of innocence" does not have anything to do with what is or is not allowed under law - it merely contends that if you are accused of a crime, you are presumed to not have committed the crime until proven in a court of law (with a jury of your peers).
Presuming innocence doesn't mean you can't be "detained" forcibly by the plod for looking odd. They are not a court of law. Perhaps that's what they fail to understand?