Jiminy

++ 1 for this solution, thank you. Having removed the driver's seat and checked all the wires after the dealer suggested the issue was with the seat loom, I found nothing wrong. Popped off the concertina door wiring connection seal and lo and behold the yellow wire was in 2 pieces and its neighbour the brown wire had broken although the insulation was intact. Cut and resoldered both, reset the fault using Carista and the airbag light is now off. It does still come on briefly after ignition, but goes off after a second or so.