Can anyone stop an argument, if a person is exempt from wearing a seat belt on medical grounds and has a certificate to say so, does that person if he gets stopped by the police, have to tell what the medical grounds are.
I say they don't because it is between you and your doctor what your medical condition is.
No, they do not, if they have an exemption then that is enough. However If they do not actually have the certificate then plod is entitled to inquire further.