Parliamentary Voting System and Constituencies Bill

I have not followed the issue of prisoner voting very closely, so I would be grateful if my noble friend could tell me where, if prisoners are successful in getting the vote, their vote would be. Would it be in their constituency, if they have a home somewhere, or in the place where the prison is? I ask this with some feeling, because my former constituency held one of the biggest prisons in Scotland and even with a 22,000 majority I would have been a bit nervous.