Depends who is putting who in jail and what is their definition of an offender.

Regarding giving prisoners the vote; I naturally despise everything emanating from the EU by default, but who should decide who can and who cannot vote; the people, the majority, politicians? What is to say the boundaries do not get changed. Maybe people who speed in cars should be banned from voting. Maybe people who have been in jail cannot vote for one year or why not ten years. Who decides where this arbitrary line is drawn?

Better, more durable, is to let everyone of maturity and sound mind vote.  Those languishing in jail may have a better understanding of what it was that got them there in the first place and vote for a better society that helps preclude the spiral of crime. 

Of cause the EU care not who votes and what they vote for since, in the EU, a vote counts diddly-squat anyway.