God - this is the legacy of the poll tax !
You are entitled to vote - the register is normally done in October and is valid for a year. So if you moved to the new address since October you can either register at your new address and new constituency, but there will be a cut off date to do it by 5th May, so you need to find out quick, or you can get a postal vote in your parents constitiency
If your politically minded you may wish to choose where your vote will be most use to the party of your choice.
As to the data protection act - I believe the register is a public document so it can be used for a variety of purposes. In the context of this site it is the key document used by credit referencing agencies to verify individuals. So it will help your get credit if you need it. It is not sold as much commercially, but it does go other parts of local authorities, and obviously MI5 and special branch. I suspect few authorities have the person power to do very much with it
Finally whatever your views on politicians - vote even if you spoil the paper see this link to remember why
http://www.parliament.uk/parliamentary_publications_and_archives/parliamentary_archives/archives___the_suffragettes.cfm