There are lots of ways that people can be traced, some very simple indeed. I typed my own name into a search engine and found lots of sites that gave clues as to my whereabouts. Then there are electoral roles, telephone directories, etc. By the way the DSS knows where just about everyone is. You are either paying NHI or claiming, but they do not give out this information. That said you might get lucky and slip through the net, even though you do owe the money, and are just playing hard to get.