Right gents, but of an update.
I now had my CODE light go out as it should, but there was still no power to the fuel pump. Checked the cut off switch and all was good, so back to the wiring diagram and found the fuel pump went through part B of the same connector.
I found there was 12v coming out of the ECU to the pump, following the wire I found it also went behind the sound deadening along with the CODE wire. Thinking that the connector was under there, I took the seats out and also removed the carpet (sounds drastic but it needed a good clean and the miserable wet weather did not disappoint
). I followed the wires back out from the soundproofing and were tucked away under the centre console were the rogue connectors G133A and G133B, next to the diagnostic plug. A quick clean to both and I had power to the fuel pump.
Next problem was the fuel pump was knackered, replaced that with a used unit and the car burst into life at the first turn of the key for the first time in five years.
I have attached a picture of the offending connectors as it seem corrosion here will immobilise the car and doubtless confuse people into thinking it is a much more serious problem, and it will hopefully save others from pulling too much of their Bella apart.
Hope this helps guys, and thank you to Henrik for his help with the wiring diagrams, much appreciated sir!