Question Author
The development of this thread since I last looked at it is intriguing. That there are/were four removed answers (what on earth was in them - the question was not designed to draw in undesirables) is to me astonishing. If only everyone had jno's clarity of vision (only one thing missed there: I wanted to contact the security people, not the airline). I failed to uncover a way to contact the search people from outside the airport but my sample of dry mineral powder/dust went through without comment. The situation varies from country to country but, presumably due to the customary lack of accessibility and openness in Britain, it is more difficult to get hold of people "behind the scenes" here than in many other countries. At Edinburgh and (some/many) other UK airports it is apparently now impossible to penetrate the wall of recordings designed to keep you from talking to anyone, which amounts to a lack of (reduction in) service. My attempt to reach the police was made as the last remaining menu choice on the airport's telephone system and in the hope of getting from a person there advice on how to speak to someone at airport security, not ask them anything about allowed/permitted items, any more than asking airlines or ABers.
The worst that could ever have happened was that my mineral would have been disallowed. What I was proposing to carry was not a secret of any kind but it was not relevant to my question and, at the point of search in the airport, quoting advice from AB would have cut no more ice than an answer from any airline. The trouble with the published lists of allowed and prohibited items is they are not a definitive list - i.e. they (deliberately ?) do not form the whole story and instead potentially leave you in the dark and the final decision to the staff. Hence my desire to ask directly rather than "suck it and see". In particular the prohibited list(s) can be read as being "not limited to...", while sometimes the allowed list actually says something like "...but you may still not be allowed...". It is at least difficult if not practically impossible to compile a comprehensive list plus the authorities presumably want to retain the final say. All of this is a good reason to attempt to get the most reliable advice - "from the horse's mouth".
Unlike some scenarios implied in this thread, there was nothing dark involved but I am acutely aware (too many examples to mention) that a person with power can and sometimes does make an ill-informed decision which then cannot be reversed even when wisdom illuminates the situation - all because a face needs to be saved and/or "respect for authority" maintained, as opposed to an admission of error becoming evident. Hence the "...you may still not be allowed ...".
I can never understand why when I go to a shop and ask if they stock something in particular (i.e. a very specific item, say an electrical plug) I am then asked what I am going to use it for even before I receive a simple yes or no (you may doubt me but it happens almost everywhere except at the supermarket). What I want in such situations is usually/always a simple yes or no - a helpful suggestion of an alternative if the first choice is not available is appreciated. Similarly, if I ask a question on AB I most of all want a direct answer to the question, although I am not against genuine attempts to be of assistance - so long as they are directly relevant. I am grateful for all such replies to my OP.