You have received lots of different advice in the above posts. Some of it quite technical and some very scholarly. But in the end it is just advice from people you don't really know who are posting on an on line forum and who have no personal stake if you should be arrested. Or worse. In the end it seems to me that if you want an answer you can trust you should get on the phone to the areas you are concerned with and get an answer from the people who could arrest you. And, if it comes to it, you might consider taking an example of a Sgian Dubh to them for an on the spot decision.
Just my humble opinion.