Best practice for dealing with electoral district / constituency?
It sounds like you want to look at the Electoral API extension and at Using CiviCRM for e-advocacy more generally.

The Electoral API extension is in beta - we have it in production for a few clients.  However, we haven't written support for any APIs except the New York Times and Sunlight Foundation, which are both US-centric sources.  Please feel free to extend it to work with UK-based sources!