The information requested falls within the responsibility of the UK Statistics Authority. I have asked the authority to reply.
Letter from Karen Dunnell, dated March 2009:
As National Statistician, 1 have been asked to reply to your question asking what the estimated percentage of the electorate on the electoral register is in each local authority in the UK ranked in descending order. (260165)
ONS do not have information on the number of people eligible to vote. The closest approximation to the figures you have requested is the number of people who were registered to vote in Local Government elections as a percentage of the estimated resident population aged 18 and over. The table shows this for each Local Authority in the UK in 2007. This is the latest year for which estimates of the usually resident population are available by Local Authority. A copy of the table has been placed in the Library of the House.
Care should be taken when interpreting these percentages. There maybe an underestimation in some areas, as not everyone who is usually resident is entitled to vote. For example foreign citizens from outside of the EU and Commonwealth are not eligible to vote.
Conversely, for other areas the percentages may be over estimates and, in some cases, exceed one hundred per cent as figures for the registered electorate may be inflated. People who have more than one address may register in more than one place (e.g. students may register at parental and term-time addresses) and electoral registration officers vary in how quickly they remove people from the registers after they have moved away from an area or died.