Indie, your GP will only know the answer if he has taken some blood off you in the past and has requested something called a 'Group & Save'. Other blood tests don't type your blood group.
One alternative is if you give blood donations then they will know your blood group and will tell you straight away.
Curiousity mainly. Plus I want to donate blood. Just thought I'd do some background research first. Turns out I can't anyway because I have a recent tattoo.
Will it say on my birth cirtificate or anything like that?
No, your birth certificate doesn't record any details like that. If you are ever able to donate blood they will tell you your blood group, usually on your second visit. Otherwise, you'll find out via your GP or if you were ever admitted to hospital and required a blood transfusion (hopefully it won't come to that though!).
well I did recently go to hospital but I'm pretty sure I didn't have a blood transfusion. I was unconcious though so I don't actually know. Hm....think I'll have to just go to my GP and try to find out. I didn't realise it'd be so difficult!