Interestingly enough, in my first year of uni I was accidently on two electral rolls, as my hall of residence automatically put everyone on. It was a general election so it is illeagal to vote twice (I was lead to believe, i'm not an expert). I phoned up the relevant person at the city council to tell her that I wasn't allowed to vote. Her advice to me was just not to turn up, which i protested about as I didn't want to be part of the apethetic 70% of the population who don't vote. My local council now at home has had the sense to only grant me votes for local elections as you are allowed to vote in two places at once for local matters, but it took them 5 years to realise this.