The Data Protection Act 1998 requires every organisation that processes personal information to register with the Information Commissioners Office (ICO), unless they are exempt. Failure to do so is a criminal offence.
There are more than 370,000 registered data controllers. The ICO publishes the name and address of these data controllers, as well as a description of the kind of processing they do. You can view a current register entry online at: http://www.ico.org.uk/what_we_cover/register_of_data_controllers.aspx