As far as I know, as long as you are not threatening the lives of anybody, you can say just about anything. The classic example of what you can't do is suddenly scream, "FIRE!", when there is none. Of course, if you talk offensively, expect someone to eventually respond depending on what environment you're in. The UK overall seems a lot more watched and under control than the US from the documentaries I've seen. Don't you guys have cameras literally everywhere?