The UK Data Archive (UKDA) is a resource centre that acquires, disseminates, preserves, and promotes the largest collection of digital data in the social sciences and humanities in the United Kingdom. If you have difficulties using it, there is a whole load of training material available at TRAMSS (Teaching Resources and Materials for Social Sciences - apparently). TRAMSS recommend you have "about an hour or so and an understanding of multiple regression" to get the most out of the site. There are just so many good resources out there with bad acronyms.