It does not come down to 'luck' if you carry a s139CJA88-compliant pocket knife or tool. Discretion [or 'luck' if you prefer] is only an issue if you commit an offence in the first place.
Absolutely. There is law and there are crimes and criminals, but if you are legal, you are legal. It's not grey, it's black and white.
There are very few knives that are classified as weapons per se. If you are not carrying the knife as a weapon and dont either intend to use, or use it as one, then it is not a weapon - it's just a tool with a sharp edge.
If you are a member of a re-enactment society, and have a 3 foot sword in your hand during a mock battle, it is not a weapon either per se or otherwise - because you do not intend to do harm to another - you are legitimately and peacably "mocking" battle - there is NO CRIME. There is no court in the land that will convict you for posession of an offensive weapon under those circumstances.