I think that's mainly for the Customs area (not that I can see anyone taking photos in the baggage hall - unless they're designing sets for the Generation Game!). It's the same at the security area; I've already interpreted this as "no photography in the security area" (again, understandable), but I notice recently that it reads "no photography beyond this point" in some airports. I still interpret it my way; it just sounds better.
Is there anyone from BAA who could comment on the rules; it really would be helpful if people knew where they stood, from a legal standpoint. If there are rules against photography, we should know where they are applied and why they are in force.