He can stop you at any time without reason if you're driving:
http://www.homeoffice.gov.uk/police/pow ... d-traffic/
Traffic law is different to what you're thinking Danny, where a copper stops you on the street. They need a reason to stop search/account you, and can't just stop members of the public without reasonable grounds or suspicion.
I have seen plently of cars being driven by idiots and just wished the police would give them a bit of a hard time. He's probably being reasonable, but plenty aren't. Subtly tape recording conversations if he does pull you is the safest way, as if he does everything for the right reason then you accept the penalty, if he doesn't you get off with it. My step-father failed the attitude test one day, and they said 'either you say sorry to us or we'll say you were on your phone.' They ended up giving him a ticket.
Touche.... We're a little more strict (or restricted!) than our civil counterparts, it seems.