A write to vote

Peter Lilley says that people in prison have no right to vote. The thought of a person in prison because they raped a nine year old child evokes intense feeling of anger and makes it a little easier to go along with the views of Peter Liiley. What about a 19 year old suffering with acute psychiatric problems in prison for stealing or fighting when they should really be in a psychiatric unit being treated for a compulsive disorder. Or a 76 year old in prison for not paying their council tax. Should we deny them the vote for being victims of circumstance?  I think it would be a good idea that your right to vote when in prison depends on the crime you commit.