Group 4 security

[mathspete]

Whilst on my recent holiday to Northern Ireland, we had to take the short ferry crossing from Cairnryan, at the security check I was asked if "I had anything hazardous on board the car e.g. extra fuel or fireworks" well I didn't consider my 17 and it's separate ammo as hazardous so I said no, and was waved through. On the return however the group 4 employee had obviously seen the gun case (in plain view behind the drivers seat) and she asked more questions about "sporting goods that could be dangerous" I said I had a legally held rifle on board being transported as per police guidelines. You'll have to pull into that shed over there I was told, I had to wait until the large door was opened from inside and then closed behind me. I then had to produce the rifle and my licence and show her which one on the list it was and that the numbers matched, while she filled in a form with all this info and then how many rounds of ammo I was carrying. My question is " what is the legal position of this search? What could they do if I hadn't got my ticket with me to prove ownership, are they entitled to check or even confiscate firearms as they are not police. Also what possible purpose did it serve as no one is allowed on the car deck in transit and the case was covered whilst I was not with it, and why was I sent and kept in a search shed and made to feel like a naughty boy because I was carrying legally held sporting equipment.