Hi mate,
If the car is equipped with PAS then it will be tested as part of the MOT, so if its not working then it should fail. HOWEVER, its more difficult to tell if a punto has PAS than with most cars, so if you get a tester who doesn't know much about puntos (and you manage to somehow stop the warning light from showing) then they may well think it just doesn't have PAS and get away with it.
Hope that helps,
Alan