I think I'm wasting my time here, and Brick his too.
It is perfectly obvious when information is classified, the security classification (as a minimum) is printed top and bottom, front and back.
WHY it is classified is of no relevance whatsoever to this, or any other OSA case.
The location of the meeting is irrelevant. I would assume that the officer in charge of cleaning contracts at MOD Main Building has his meetings there. It does not follow that he is authorised to take the head cleaner into the commcen and say "where's your camera, the juicy stuff is in that filing cabinet over there".
I don't mean to make light of this, it's a vital principle of military life.
Careless talk costs lives.