In reply to pec: our airbag light was on when we bought the car, never bothered me really, I've had plenty of cars without airbags, and the ones I've crashed with airbags, they've never deployed!
regarding the MOT, an MOT tester is not allowed to remove anything from the car, so if you stick a piece of black insulation tape over the airbag warning light, they then can't see the light, and in theory, can't fail it... gotta be worth a try!