FIXED
Bought a new pump - wasn't sure if it had broken or not but figured by the time I have the wheel off, arch liner and access to pump I might as well have one to hand if it was faulty.
Turned out, the pump was a funny colour in certain places... it was definitely not functioning properly... anyway, fitted new pump as per below and worked perfectly again. New pump on left, old on the right - reservoir draining in the background
