Cheers for the reply.
I have checked the ecu and there is no flash codes coming from it. I've tried replacing the ecu with a known working spare that I had laying around and it didn't fix the problem.
I've bled the system and theres definitely no air in it.
I had to drive the car for 20 minutes prior to doing the bleed just so that the pump would work when I unplugged the connector, that runs the pump, to perform the bleed.
If I unplugged the bleed connector when the car is cold, the pump does not run.