About a year ago, the Canadian government proposed that anyone who had visited the UK at all since 1980 would be banned from giving blood. Until they realised that it would remove approximately 50% of all potential donors.

Secondly, why six months? The current research suggests that you may have been able to get it from a single meal. Thirdly, why didn't they do this 5 years ago? I don't really see the point in such a half hearted measure...