Parliamentary Voting System and Constituencies Bill

Before my noble friend sits down, would he answer a question for me? In looking at his calculation of how many additional prisoners would be entered on to the electoral roll, is he aware of any estimate of how many prisoners were not on the electoral roll prior to them going to prison? There is a case to be answered that a number of prisoners who get into a life of crime lead somewhat chaotic lives and may never have voted or be on the electoral roll in the first place.