The following is the advice the dealer obtained from Vauxhall Tech, relayed to me on the phone. I can make no claim as to it's accuracy as I didn't speak directly to Vauxhall Tech myself, but have no reason to doubt it as I'm sure they'd do chargeable work if they could!
The front passenger airbag cannot be physically removed nor can it be programmed out individually with tech 2 - they declined to say if this was a technical limitation or a liability issue. When I enquired about retrofitting the front seat occupancy detection system for use with a Vauxhall child seat I was told that; 1. It would be too costly (£2k +) and 2. They wouldn't do it anyway for liability reasons. So if the vehicle does not have the ability to detect a transponder equipped child seat then no rear facing seat of any kind may be fitted in the front passenger seat.
I asked would they disable the passenger airbag system if I were to sign a disclaimer, in the same way as VW dealers are happy to. The answer was no, they would not, no exceptions.
The outcome was the dealer gave two choices:
1. Don't use the car to carry infants.
2. If the ability to carry infants in the front is a requirement, get a replacement vehicle with the appropriate features/options installed from the factory.
In the case of an Astra or similar, if there is no system to disable the front airbag on the car from the factory (either by a keyswitch as found on the newest gen Astra or transponder system) then the front seat must not be used for infants - only the rear seat will be available for this purpose. Dealers will not intervene in any way to alter the vehicle to make it suitable.
I was also warned it may be illegal to modify the safety systems on the vehicle as it could potentially invalidate the insurance.