When you say you "asked them [the blood donation centre] already" what do you mean? You can't just ask them to find out your blood type, you have to actually give blood. If you're able to give blood, I'd reccommend it. You then get a letter stating your blood group and any problems (deficiencies etc.) they may have found in your blood.
just give blood, i did this a couple of weeks ago and found out that only 6% of the population do - shocking! so if you can, you really should. just remember not to go out on the tequila afterwards because it's really really not good for you. but i recommend it, considering that it will really cause no inconvenience to you at all and may save someone's life. plus you find out what your blood type is and also get a cool card thing
yes i've given blood (even though i am willing), but they are not able to accept because i wasn't born here. so i didn't find out what blood type i am.
Your GP won't do it to satisfy your curiosity...only if there's a medical reason. You can however ask them to do it privately. That should cost you about �40.