It may well be in your hospital records but not your gp record. I have never worked as a GP so have only a working knowledge of their system, but it's definitely in your hospital notes. The reagent card tests aren't expensive and are pretty accurate for ABO Rh grouping, and only a few quid online. But only if you follow the instructions to the letter
Requesting your records can be done by writing to the trust, but 99% of hospital staff will show you them informally if you're there. They charge an admin fee for accessing your records
Thanks again, mick, all useful information