It's named passive immobilisation but once the fob works to unlock that will certainly remobilise it if there's not some other failure, the BCU works with the remobilisation coil through the RF receiver

Howsit guys

So some feedback regarding my issue. It turned out to be the RF receiver as predicted by sirrafery. I bought a second hand one locally, disconnected the battery and fitted the spare. Five minutes after reconnecting the battery it fired right up.

Many thanks to you sir, your patience and knowledge are very well appreciated.