The only place I've ever seen police boxes is in Edinburgh. Some are now used as police 'info boxes' (with a computer touch screen thinghy), others have been converted to coffee-vending booths.
I have a feeling Boolbar really wants to get this one...
I'd like to offer a hint without giving the game away, but I'm finding that difficult so I shall say for now that the the last three guesses are quite cold.