Jon,
I don't want to sound rude, however any knife that is longer than 3" and/or has a fixed blade is illegal.
As bushcrafters we don't have a right to carry them, but they are classed as tools, so if you have a bushcraft knife and your on your way into the woods, have it at the bottom of your bag, then get it out when you make camp. There is no reason to have it on your belt in Tesco.
Like I have said they are illegal, however there is a defense in law, and it is for YOU to prove that you are innocent, not the police/courts to prove your guilt.
Your right the Police cant just search you for no reason, however they can ask you to give reasons for your actions, ie where you have been or where your going. If you become all "shifty" and they believe you have in your possession something you shouldnt have, they can search you.
When I go bushcrafting, I have an axe, folding knife and a fixed blade, they are all packed away in my bag, and come out when i get there.
I have experience of violence with knives and NOT once was it a bushcraft knife, however these are our laws and we have to stick to them
On a final note, if you are stopped by the police, be polite and explain what your kit is for, if you become all defensive they may take this as you have something to hide...
Ta
Woody...