Or the relay could be faulty.

 

BCU only interrupts the trigger wire to the fuel pump relay if there is a security issue, but you said the relay trigger wire is being energized right?

 

I'm not sure on the trigger wire but i have been told that when a multimeter is applied to the fuel pump relay and the ignition is turned on to pos II - 12v appears at the relay and then goes away when switching off the ignition,
I'm a complete electrics novice and rely on others with the knowledge.

Would it be worth switching out the bcu and ecu for another matched pair- just to see if that works? I'm led to believe you swap over and turn the ignition on for 30 mins to sync then start the car?

 

95% of automotive electronics can be done with nothing more than a test light, you have voltage/light or don't. Simple as that. If you have have voltage on the trigger wire, and the relay works, it should energize the connector at the fuel pump. If it does not, you have a break in the wire between the relay and the pump.