I can fully understand the matter of snapping at a military base as there is still some trouble going on over in N.Ireland. A rather odd thing for a train spotter to be doing I think? On the other hand to be fair many of us would probably not think! Indeed I can admit to such quite innocently at the time. Many years ago. it was away back in the early days of the 'Trouble' and I was on holiday over there and just off a city centre street was a line of army vehicles having a rest. So I thought "wow, a great picture". Two armed squaddies came over and asked me to accompany them to their sergeant who was talking with a Major. Turned out he was Scots and pleasantly asked my reason for the picture so I explained. He smiled and took the camera and pulled out the roll. They were quite good about it. It should remembered I was coming from somewhere without a problem and would have snapped away at Edinburgh Castle guards and such.
In my present project on doing the NIR system (even from Glasgow!) I have been over taking notes and occasional photographs to remind me of special items to note. However where I was at a staffed station I asked, explaining what I was doing and showed an ID. No probs and at one important station the manager couldn't have been more helpful. Someone else put me in touch with a man with a website full of NIR train pics who in turn gave me a link to someone with a driver's eye view of a mothballed line he had got permission for in 2002. Doing it by foot was impossible due to the geography. Elsewhere with unstaffed Halts and stretches in rural places I just got on with things. Where I need to have another look I can in most places but not all, use Google Earth. However there is one area I need to suss out and will pop back over but always use common sense and ask before I do anything.