I have given blood a few times in the past and decided that I really ought to start doing it again. It generally gets you a free cup of tea and a biscuit if you like that sort of things and makes you feel like you're giving something back above the usual taxes.
I checked out the givblod.dk to see where and how I could sign up and then whilst checking the restrictions on who can donate I found this:
OBS: Har du været i Storbritannien samlet i 12 måneder eller mere i perioden 1980-1996, medfører det karantæne indtil videre på grund af en teoretisk mulighed for overførsel af kogalskab (variant af Creutzfeldt-Jacob sygdom). Storbritannien er her forstået som England, Wales, Skotland, Nordirland, Isle of Man, Kanaløerne, Gibraltar og Falklandsøerne.
A rough translation is that if you have been in the UK for a total of over 12 months between 1980 and 1996 you cannot give blood because of the risk of infection if mad cow disease.
I was absolutely amazed by that and now I feel like I am being discriminated against!