This has been known about for quite a while, you can find out more
here about opting out.
Mind you, if your of general good health you may be concerned, but if you do suffer from something or perhaps are a biker, then having your medical details
instantly available at all hospitals etc can be seen as a good thing.
(Security concerns aside - that is).
P.S. anyone wanna buy a copy of the database? - its at www.nhsdatabaseforfree.com