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possession of knives in public are generally dealt with under 2 different laws - that governing possession of offence weapons and that dealing with bladed articles.
re the former, unless the knife is designed as a weapon (some tactical / specialist killing tool or with a knuckle duster hand grip for example) it's only considered a weapon in law if you have it with intent to use it as a weapon.
re the latter the law is simply designed to stop people carrying bladed (or pointed) articles in public for no good reason - you don't have to have a criminal intent to be guilty of this offence - but you do have to have a good reason to avoid criminal responsibility. there is no definition in law of what amounts to a good reason, the court (if you are prosecuted) will decide on a case by case basis. this law covers articles with a blade or point, except folding knifes with a blade of less than 3 inches. as a matter of law, blades that can lock in place are not considered folding.
If it gets to this. Once you've had your knife confiscated by the Aged William, cautioned and told you will be reported for an appearance at court; you present yourself at court in front of a magistrate or it could end up in front of a judge and jury at Crown Court. There are so many factors to be considered that it is a minefield for all sides. If you're stopped in an area where there has been knife crime and you have an illegal knife in your possession then it is unlikely to end in your favour. It's all down to attitude on both sides of the initial interaction (and CPS advice) which decides if you go to court. It is then down to the court to decide if your locking Opinel was purely for your innocent food carving or not.
A factor in your favour is the accessibility of the weapon. If it's really wrapped up and difficult to get to then that would imply that you do only "cut the cheese" so to speak.