There is a key issue generally ignored in this debate. It's not so much about the rights of the individual prisoner but the wider consequences for collections of individuals.
The demographic of prisoners isn't representative of the general population. For example, blacks are grossly overly represented. Thus denying prisoners the right to vote can impact on the voting strength of minorities.
The major imblance in prison populations is of course between men and women. 96% of the prison populaton is male.
Men are already a voting minority given that the population of males over 18 is rather less than women over 18. The constant growth of the prison population means that this voting imbalance is steadily becoming greater (the proportion of female prisoners is actually decreasing : In fact, the government recently stated that no woman should be sent to prison :
www.bbc.co.uk/news/uk-13666066).
Furthermore, increasingly the laws that result in men being jailed, and consequently losing their voting rights, are made by women, and sometimes even only apply to men (for example the law against having sex with drunk women).
Am I the only one who can see anything up with this?