I was just reading a similar post, but it was a couple of years old, so starting a new one.
I walk my dog around my estate, so I see more people than most. I have noticed that some houses are empty. I don't know for certain, but a neighbour was telling me that one guy that has had this flat for a year or so, he lives 5 miles away with his girlfriend. I talk to the guy that lives in the flat above, and he rarely sees or hears him.
I notice other houses, where I vaguely know who lives there, but they are never home, I suspect that they live elsewhere too.
Is this something that others have noticed. Most people just get in their cars, so they wont notice who lives where. I did report the guy that lives in the flat, but its not easy for the council to prove he isn't living there.