I've said this before on a couple of previous posts on the same subject.
It's my theory that these people are the modern day equivalent of train spotters, but they collect bank sort codes instead. They loiter around cashpoint machines collecting discarded slips of paper. They all wear ratty old track suits tucked into socks, cheap anoraks, jam jar specs, and the men usually have a comb over. They usually have some arresting physical defect, and dandruff and BO are de rigeur. When the banks are closed they sit hunched over their PC's with a thermos flask and a fish paste sandwich, waiting for some sucker on Answerbank to tell them the address of a particular sort code. At this point they are transported to a state of sheer ecstasy as they can add another one to their note books.
Well, that's my theory....unless someone has a better one.