Red Tamarillo wrote:
I just did a brief google to remind myself of your UK laws, seems like a folding (but not locking) knife with 3" blade is legal (as long as you have a reasonable excuse). But butter knives classified as offensive weapons/blades (from a Charlie Booker 2005 case).
IANAL, so for entertainment purposes only, but that's a bit mixed up. In the UK there's the law on carrying knives (primarily CJA S139) and the law on Offensive Weapons. First, I'll mention that "self defence" is generally not a good reason or reasonable excuse so far as these laws are concerned.
Now, CJA S139 requires you to have a good reason (or lawful authority) to carry a bladed or sharply pointed article in a public place, but makes an exception for (non-locking) folding pocket-knives with a cutting edge of less than 3 inches.
Any item that is made, adapted or intended as a weapon is an Offensive Weapon, and cannot be carried without Reasonable Excuse (or lawful authority). Certain semi-banned items such as automatic knives are also considered de-facto Offensive Weapons. Now, this law can in theory apply to absolutely anything, and could apply to a S139-exempt pocket-knife, but unless the item is made or adapted to be a weapon, they'd have to show intent (for example, if you were to unwisely say it was for "self defence").
So, assuming you have no intent to carry anything as a weapon, you can generally carry an ordinary sub-3-inch non-locking folding pocket-knife in public just because you want to, and most other knives and sharps if you have a good reason to do so (for example, to use them for some lawful activity).
Also the case above (the knife/"weapon" searches) was in Australia, not the UK. I believe the Aussie laws on knives are generally even more strict than UK law.