Today, as the weather was nice, I decided to have a proper look at this.
I got my meter out and checked the front sensor for continuity, there was none. I inspected the end of the sensor and saw what, I'm hoping you can see in the images below. It looks like the side of the sensor has worn. If you look, you can see that the sensor has a fat side and a flush side. I think the person the fitted the pads must have fitted the sensor the wrong way round.
I cut the end off, shorted the wires together and hey presto, no more "brake wear". After 7 months of this flashing on the dash, when I finally got round to looking at it properly, it took about 30mins from start to finish, and that included jacking the rear of the car up too to replace that sensor.
Thanks for all your advice.
Mike