| Forgot to come back with the resolution: the problem was tracked down to a faulty antenna. It's a coil of wire inside a plastic cover around the ignition switch that detects the signature of the key being used to check it matches the one the ECU has been programmed with.
Apparently someone prior to me had done a dodgy repair job on it and used some type of glue that had destroyed the insultaion around the antenna wires and therefore the ECU failed to recognise the key and therefore shutdown. I should have read the instruction manual better since there's a procedure detailed in there to bypass the security check if you know the right codes etc. so you can get home. | 
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