Sorry i haven't updated this thread, but thanks to everyone who have replied. I took the rear caliper off the other day and had a good play around with everything. The sliders "seemed" alright, but they weren't sliding massively smoothly and they had a couple of uneven bits on them. I scrubbed them hard with a cloth to get them clean and shiny again, applied copper grease to them and put some copper grease in the hole and made sure they were sliding cleanly.
The pad seemed ok, although to the eye you could see the difference between the part that had been making good contact, and the part that hadn't - the part that hadn't was a slightly different shade of colour. There didn't appear to be any lip on the pad. Anyway, i refit everything and the brakes seem as good as ever, so i'm just going to see if the rust wears down now that everything has been reseated, i hope it does, if not - i guess it'll be new pad and disc time!