I gave blood for the first time this new year in the UK, you have to fill out a survey saying if you've ever come into contact with people who are at high risk, i.e. hookers and junkies, and seeing as I've lived in China, Africa and the Middle East in the last five years and have a job where I have to be tested for HIV and hepatitis to get work Visa in such countries there was a couple of times where I felt they would reject me but all they did was tick the appropriate boxes and they took the sample anyways seeing as they will test the blood before they use it. Me having tested negative for all blood diseases just two weeks prior made them worried as I guess they thought I could have picked up something getting tested.
And I've had tattoos done in the US, Thailand and China and they didn't seem to care about that so I'd be suprised if you "can't give blood for 12 months" after getting a tatt.