Hi Ray. I think the days of immobiliser boxes are dead. The immobiliser is now made up of several components, and without any one of them in the circuit it will not start. ( all communicating with each other through can lines )
I would think the items in the immobiliser circuit on an astra H would be. :- CIM module. Instrument pack, Body control module, and engine ecu. Also anything connected to the can lines can affect starting, i,e power steering ABS etc.