It’s helpful to quote the post you’re referring to in replies especially if the thread has move on a bit since the OP.
I attempted to quote in this post and failed.
I didn't
Now I don't either! It seems to be quite random.
Anyway, sorry about the hijack - back to the actual discussion.
I imagine (and I could be wrong!) that some cases are clear-cut- people have a known and officially registered disability, etc, and they will be exempt if clearly over the 40%. Other cases will be borderline and will probably have to attend assessment by military doctor, with medical dossier and info from treating medics. Same for unusual cases (as for my GS, very severe life threatening allergy- but fit and strong). My understanding is that if they have genuine medical reasons for not serving in military, but fit for civil service, they won't pay tax.
If people choose not to serve, then they will pay.
To be confirmed.