First of all, one must pass the medical examination prior to operating on the line, has there been a problem with pilots passing the initial screening? Not too much, occasionally a pilot will have to take care of some particular issue that may create a small delay.
There have been a few instances of pilots failing the medical after being hired, very few.
As far as how the exam is administered, please read the thread, someone has already posted a good description.
Sorry mate, no CAA here I'm afraid.