Thanks for the tips guys. I popped the calliper off today and there were a multitude of issues.
The calliper had a lot of crud in it and the pads were catching on the sides, so I gave the runner portions a good clean and scrap out with a blunt screwdriver. I also took a file to the sides of the pads to get the crud and surface rust off.
I Then followed your guide for doing the pistons fuzzy, except using brake cleaner instead of kerosene/brake fluid. Took ages to get the pistons to spin to do the back, but I got there
Put it all back together with some liberal pyroplex grease, then copper slipped the back of the pads and built it all up. Also a fair bit of crap on the pins for the pads, so gave them a wee rub with emery too before greasing.
I did your tip as well punk sting and attacked the brake lever pin with release oil, then oiled it with some light oil.
I've not had a chance to get out and test it yet (but I will be leaving for uni soon so will get a good 30 miles to check everything), however, even just on spinning the back wheel and pressing it is night and day, so it appears to have done the trick.
Thanks again