If you've a wiring diagram, you should be able find where the installers have cut into the loom for the immobiliser.
Given that the only circuit which is unaffected is the hazard circuit which would be needed for the operation of the alarm system, then its likely that its the alarm/imobilizer system that's faulty.
If you've the Kent engine with a mechanically driven fuel pump and a carb, then in theory the only wires the will have cut into is the switched feed from the ignition switch to the starter solenoid and the coil. These wires will be white/yellow
Hope this helps
Arwyn
