It is always a thought provoking topic that's for sure, but you nailed it in one statement . "We have to legislate for muppets"! Most of us that carry a knife are sensible about it, we treat them as tools and not toys or weapons. The guy you related to that had his knife taken off him on the train .. well IF he was really sitting on the train shaving his arm, then he's one of the aforementioned muppets. Over in the US I had my Swiss Army Knife taken off be by the thugs that run the Liberty Island security. You have to to go through airport style security and I'd genuinely forgot it was in my pocket. My options were 1) hand it over for destruction or 2) Turn back and miss my slot on the boat over and thus losing my money for the trip. It was a $30 knife, if I'd been alone I'd have just left with my knife, but the trip costs were over the value of the knife.
I find the UK knife laws, like a lot of laws that relate to "weapons" laughable since the ONLY people that try to adhere to the laws are the law abiding citizens. Criminals will never pay attention to them and those are the very people the laws are designed to try and stop. Law makers really just don't get it.
As for the carry of bushcraft knives. I've read over and over and I practice this myself, my bushcraft knife stays in my ruck as far down inside as I can get it but still make it accessible so I don't have up end the bag to get it out, but far enough in to make it difficult and show PC Plod that I'm not ready to use it in a seconds notice. Do not carry on your belt in to and out of the woods. Get to your camp spot then strap it on if you must. I don't see the need at all for "bushcraft" knives with 10+ inch blades like that beast you have haha a smaller knife and an axe will be a much better replacement. It would be much easier to argue the reasons for having a small hatchet/small forest axe and a sensible knife over a 15" machete.