Many thanks mate for replying so quickly, much appreciated. May take a look.
I do infact also own a PDA (Dell Axim), and have TomTom 6 installed (GPS Satellite Navigation software). This also includes a very recent version of the UK Traffic Camera Database, so it alerts you as you are approaching a speed/traffic light camera. It's proved invaluable!
BUT... I'm quite interested in a passive device also, as GPS devices won't detect mobile cameras... ie: a mobile police camera van parked up somewhere, or Mr policeman with a speed gun!