legal advise

[rustyrider]

The MoT tester isn't allowed to dismantle anything to inspect it so if the pads are visible with the wheels and dust shields in place and he can see that they are very thin, he can advise on it (but not fail if the braking efficiency is still OK).  If he can't actually see them, as ferritt says, they can be down to fag paper thickness but will still pass if the braking efficiency is up to standard.