Posting here for traffic...
I've just realised that the council sell our details (supplied to the electoral register) to companies and charities for marketing purposes. They add your/our details on to something called the Open Register without consent and it's up to individuals to ask to be removed.
I think it's appalling. If you'd like to have your details removed, go to your local council website and search 'remove from open register'. I'm going to formally complain too and urge you to do the same. I think if you're going to use people's data to make a buck you ask them first, not put the onus on them to opt out..