Uh, no, the cops can't come in and have a look without a warrant, not in the U.S. At least, not if you don't let them. In fact, they can't even legally scan your home with infrared heat detectors without a warrant. (SCOTUS already ruled on that. Scanning someone's home for heat signatures, in and of itself, constitutes a search, and is thus illegal without a warrant.) I don't know anything about how the UK works though.