Correct me if I'm wrong, but isn't a locking pocket knife, despite being much safer, an illegal item to carry? As is any length of fixed blade when in an urban area? Isn't it true that knives with points of any blade length have been banned, or their banning discussed, in that various Parliaments of the United Kingdom?

Is not the determination of "good reason" left at the hands not a jury, judge, or prosecutor, nor defined by law, but an individual police officer? And that can be applied to any object in a person's possession? By your own admission, that can be applied to most any item, even a flashlight.

Oh my- what if a police officer decides you don't need a camera or cell phone on your person while walking past a jewelry store or bank? Or that your umbrella could make too effective a weapon in the wrong hands?