Hi Rich,
Thanks for your response. When the key is turned to the start position, the starter does not engage and there is no feed being switched to the starter contactor, as there is no voltage drop and the panel lights such as the 'low air pressure' and the gauges do not dim or fluctuate. The battery charge state is good, the batteries are connected correctly and I have tried it with jumper batteries connected. The voltmeter on the panel at the helm shows 13.5 volts with the ignition switched on and it does not show any less when the key is turned to 'start'. This is why I believe the starter is being inhibited either by the immobiliser or by the transmission having no power to the panel so that it doesn't know it is in Neutral.
Stefan