Thanks very much Binty.
So, an update. I didn't end up with a huge amount of successful however I did eventually manage to locate the micro switch - notably the clicking sound gave it away. Your comparison to watchmaking is near on perfect; this is a very tricky job to do. So, having depressed the switch several times and used some contact cleaner; I am in no better position so I suspect that the switch has lived its final days and a new one is in order.
Having had a quick look online for the catches, they look a bit of a pain to fit (bumper off job) as it comes complete with the connecting wire for the catch on the drivers side which runs under the bumper top edge.
Thanks again for all your help - they were invaluable
