it used to be a rule that foreign nationals had to register their address with the local police. You got a little booklet when you did that was sort of passport-ish and the police stamped every time you moved.
This was done away with, I think, around 1998 or 1999, shortly after Labour came into power. I'm not sure if that was true for all foreign nationals or not. (as a matter of fact, one of my old passports has a stamp that says I'm no longer required to register with the police, but that i'd be wise to keep my booklet.)
In any case, if your wife were required to register, she should have been told that upon entry, and it should be stamped in her passport. Feel free to ask around, as I'm only 95% sure of that. but 95% is rather a lot.
