I spent the day installing a replacement engine fan and replacing all the associated bits and pieces hence my silence.
I eventually decided to break into the fog lamps' circuit. This means when I need the parking aid I switch on the side lamps and front fog lamps. A bit crazy, but eventually I shall probably take your advice and see if i can use one of the circuits from the engine fusebox. The trouble with that is that most of those circuits are perpetually alive. I need a supply that is only alive when the ignition is switched on. I want to avoid having to trail a wire from the fusebox that is inside the driving compartment unless there is some easy way to do it without drilling holes in the structure..