The 30bht hospital thingy.
When I got my yellow book, 14 years back, we asked at our local hospital if I can get on the scheme, we knew a lady at the hozzy, so she did the enquiry for us.
The answer was no, the reason, the yellow book has an information/ID number, your number does not start (or end) with the number "_", can't remember what it was, but think "0"...
Anyhoooo, that number is the key, what ever it is..????