Thanks for your help guys, Fortunately i think i was able to diagnose the problem. I took the caliper end of the brake line off the caliper and pumped the brake. There seemed to be sufficient pressure to push the piston against the pad. So i connected it back to the caliper and pumped the brake. Still same problem with binding to the disc. As soon as i loosened the bolt connecting the brake line to the caliper a whole heap of pressure released and the brakes became unstuck. So thinking that maybe something was preventing the oil returning through the brake line, I took the whole brake line off and reversed it so that the end that normally connects to the caliper was at the master cylinder end and vice versa. I started pumping the brake and there was no pressure build up to close the pads on the disc. So my theory is theres some sort of gunk or tear in the brake line thats acting as some sort of one way valve. If anyone disagrees or thinks it might be something else, please share your ideas.