Just to follow up on this, I've managed to get a few minutes in the workshop and figured out how to remove the airbags. It's a fairly simple process to be honest.
1. Remove the adjustment knobs and side trims.
2. Remove the 2 bolts that hold the back to the base on one side (not essential, but helps with access)
3. Unclip the black plastic locking strip at the bottom of the seat back.
4. Remove the two tension strings from their clips.
5. The leather covering of the seat back will now be free to work up the seat frame, turning it inside out as you go. You can get it about 2/3 of the way up before you get to the next set of fixings.
6. You should now be able to see the airbag module. It's held onto the frame with 2 10mm nuts. Undo these, disconnect the wiring and lift it out.
I then fashioned a piece of foam from an old seat squab to the same shape as the airbag module and inserted this into the hole before re-assembling the seat.
I also took a good look at the heated seat wiring - I can see why the switches don't last very long - wouldn't have bankrupt Alfa to use a relay, surely!
So, anybody want some 147 seat airbag modules? Free, but you'll need to collect them from Bournemouth.
Last edited by daveturnbull; 13-11-14 at 10:36.