I took the top of the canister off, the bit with the motor and whatnot in it, I filled a sink with water, sat it in the sink and pulgged it in and lo and behold water came out of the outlet on the top, and quite fast too, so there is nothing wrong with the motor / pump whatsoever.
I think I've managed to isolate the problem, the water inlet at the bottom of the canister isn't letting any water in, which does explain why its doing feck all, looking at it, it does seem very narrow and not likely to let very much water through anyway. anyone had problems with water not getting into the canister?
Cheers