One the airside I quite commonly carry a sharp folding knife. A leather Man or small folding knife. While I do not make an obvious showing I am prepared to argue the toss if bailed up by someone who claims authority. My explanation is that it is a tool of trade. There have been many cases of air accidents (and car accidents!) where the seat belt jams and has to be cut to get the body held free.
Ask any Paramedic.
If one looks at any post crash report it is often mentioned that a knife was or was not included in the pilots survival kit. On the person is better than in a bag that gets lost. The same applies to an ELT. Every survival kit list has a knife included close to the top of that list.
Ask Plod if he checks in his side arm when he leaves the police station to go across the road to the sandwich shop for a sandwich. Does he check in his side arm before he leaves the station? To the sandwich shop is off duty.
So you carry a Swiss Army pocket knife? Short blade. 3" ? If Plod wants to arrest you then he should be doing same to every Boy Scout in the country. How many times have you heard of a daytime bush walker or hiker who has nothing in the way of kit for self sustainment?
The key items are a knife, a fire lighting device and a jacket or like cover to stop hypothermia.
For a pilot working in a remote area a knife is a must. But be discreate about it.
Around the big smoke I leave my knife in my flight bag out of sight when I leave airside. If travelling by airline to a location I leave the knife in my check in bag.
I recall bumping into an ADF guy at the Avalon Air Show some years back. He had a folding knife hitched in his pocket. I noted that and asked to compare notes. His knife was the same as mine. He said that he had once been bailed up by Plod or like and asked what his justification for carrying a knife was? He replied that he had been in one or two air crashes and had had to cut people out of their jammed seat belts to free them The discussion with the asker finished there.
At the end of the day common sense should prevail.
Sometimes that lacks in some people who claim authority.