It is probably worth remembering that for the offence of carrying an offensive weapon the burden of proof lies with the person carrying it that you have a good reason.
Police only have to show that you had it.
Saying nothing if you were challenged may not assist you in this instance
'Saying nothing' refers to not giving officers in the street talking to you/arresting you any additional information you are not legally required to.
So like, your name, where you've come from, what you're doing, where you are going later, etc. Police are trained to talk to people in a way to get them to self-incriminate.
If they decide to arrest you, and
after you've called your choice of solicitor, and
then are at a court - this is the time to explain what your good reason was, and give the information your solicitor advises.
Chit chatting with the bobby who is thinking about arresting you about what you are doing gets you nothing, but potentially costs you a lot. They literally can't arrest you without a reason. If they do, you can sue them. So in this interaction, they will be probing for anything you say they can use as that justification.
For example, you might say
'its for if i get into trouble or difficulty when I'm far away from help out in the countryside', and you mean
'to cut cordage into smaller lengths to rig an emergency tarp', but they have you on video saying that and what they hear is
'to stab someone in self defence' - they now have sufficient cause to arrest you, and the situation has become more complicated.
So yeah, stick closely to the script - be polite, but not chatty
- am i being detained? if no, leave the situation.
- under what power am i being detained? if they can't tell you, leave the situation
- assuming it's a stop and search: why do you have reason to suspect me specifically? if they can't give a description, leave the situation
- what object are you looking for? if they look anywhere that object cannot be, tell them and refuse consent for it to be searched
- and give out no other information
It's about trading off short-term discomfort for long-term consequences, if that makes sense. They can't arrest you on a hunch like in the movies, they have to follow procedure. They will be looking for opportunities to make their hunch procedural!
For example...you don't ask "am i being detained? under what power am i being detained? then I'm free to go", you chit chat with them, and they are very friendly and reasonable, and you mention going off into the wilderness for a few days and watching ray meares and all the great bushcraft you're learning and how much you can whip up from wood if you are in a pinch and....
now they have cause to suspect you might have a knife which is what they need to search you, and now you are in trouble.