The information requested falls within the responsibility of the national statistician who has been asked to reply.
Letter from Karen Dunnell, dated 15 January 2007:
As National Statistician, I have been asked to reply to your question regarding what estimate the Office for National Statistics has made of the number of people on the electoral register who are not eligible to vote. (114107)
I can confirm that we do not produce such estimates.
The Office for National Statistics does collect information from electoral registration officers as required by the Representation of the People (England and Wales) Regulations 2001. This requires the submission of a statutory form of factual information every December. The form does not though require electoral registration officers to make an estimate of the number on the electoral register not eligible to vote.
We have conducted an assessment for the Electoral Commission of levels and types of people not registered to vote. The subsequent report can be found on their website at:
http://www.electoralcommission.org.uk/templates/search/document.cfm/13545