Okay, found the problem.
Pulled the calipers back off and found that on the side that was binding, the key on the pad was slightly off centre of the slot in the piston and caused the pad to be squashed at an angle.
So simply slotted the pad back into the slot and made sure that while putting it back on the rotor I didn't knock the pad out again.
Thanks for your help fellas. :s4
On the plus side, my handbrake is now perfectly adjusted and there is definately no air in the brake system.