What used to be the hospital at Wegberg is headquarters of the BFG Health Service, and is mostly offices. There's a small outpatients department, the psychiatric unit, and the mortuary. Elsewhere on the site is the HQ of the service schools lot. The train testing facility is at Wildenrath.
Yes, they keep records centrally. However, there will also be a record of any surgery in your notes - if you are still serving, in FMed4; if not, in your NHS notes. Either way, you are entitled to have a copy, for which you may have to pay a small fee.
The complete FMed4 is forwarded by your last med centre to a central point (for the RAF it's PMA at Innsworth, but each service has its own store), where it's retained indefinately.
A summary is produced (FMed 133 - Medical History On Release From HM Forces), which is handed to the individual for him to give to his shiny new NHS GP. If the GP wants any more info, there's an address on the FMed 133 for him to write to - the relevant stuff can then be extracted from FMed 4, or the CD-Rom system used until 1999.
There are other records that are kept - theatre log books and inpatient hospital notes, for example, and these are also retained.