Earlier quoted context omitted.
That definition is incomplete. Threat actors also abuse this to hide their command and control infrastructure.
Threat actors use knives to stab people - we have to stop selling those.
In the UK if you're under age and you decided to buy a knife you will have a lot of difficulty unless it's a little folding (but non-locking) pocket knife, like the small Swiss Army type utility knives. Indeed legally as old as 17 you can't even buy a steak knife in England although you can in Scotland.
Once you've bought a knife, it will usually be illegal to carry it in public unless you have a good reason, and "self defence" is not a good reason.
Some particular knives, which have no apparent purpose except as weapons, are just illegal automatically except in some cases if you're a museum. In particular almost all swords (if they have a working blade) are in this category, and most things designed as concealed weapons (e.g. blade hidden in an umbrella, combs that are actually knives, push daggers)