Fuel cut-off switch? Also known as the inertia switch, or maybe what you call the immobilizer. It's designed to cut the fuel pump off in an accident. In US vehicles it's located on the right side kick panel of the vehicle. I'm not sure about RHD vehicles though, so check your owner's manual. To double check this switch: unplug it, use some solid insulated wire to bridge the 2 points on the conncector, try to start car. Do not run the vehicle for very long like this. If you have an accident, are unconscious, and your key is still ON, fuel will still pump. I've seen accidents on other vehicles without this safety feature where the fuel continues to pump out of the vehicle as fast as the pump will do it.
There is also the fuel pump controller which on US cars is located under the RH side rear seat. Lift the seat up, and you'll see the electronic controller there. Unplug and check to be sure you have power to the power supply side with the key On. If you have power there, and not power going out- that might be indicative of your problem. I think you'll find it in the fuel cut-off switch though.
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