Dicky_Boy,
I had the same problem on my A4 TDi, there was no switch in the glove box to disable the passenger airbag. There were 3 ways around this.
1. The dealer can disable the airbag by disconnecting the lead and inserting a plug into the lead that has a resistor inside it. This fools the airbag control unit into thinking that the airbag is still connected so the warning light does not come on. The price for this was about £35.
2. It can also be disabled via the diag port using vag-com. The only problem with this is if the battery is on its way out and the volts drop below 9Vdc the control unit can reset itself and the airbag will be active again without you knowing. You can get this sort of vold drop when cranking the engine over, especially on diesels.
3. I did it this way. I disconnected the passenger airbag myself and didn't bother about the warning light. After my son had grown out of the front car seat, I re-connected the airbag and had the control unit reset. As long as the ignition is switched off and you make sure you are not charged with static, the airbag should not go off.
Hope this helps you.
Jim.