Robin I agree with you and to add my own thinking:

Surely the issue for some prisoners is a matter of timing if they will or not be able to vote. I imagine that there may be a considerable delay from someone committing a crime to that person being incarcerated. If the term is less than 5 years, then we just have a timing issue and I don't think that is good enough reason to prevent someone from having a vote. For those on longer sentences they are almost sure to have an election of some sort during their term, and I would still argue that sowing a little respect by allowing someone to contribute in a positive manner in a democracy should not be withdrawn. Criminals are being punished by being imprisoned (and let us not forget that sometimes an innocent person can spend time behind bars while their appeal is waiting to be heard)

It is interesting that opposition to prisoners having a vote is larger than the proportion of people who do vote. To me that is the problem with our democracy.