Close the knife loophole!
They have actually tried that in the UK.
Carrying Knives in Public
The CJA 1988 mainly relates to carrying knives in public places, Section 139 being the most important.
"It is an offence for any person, without lawful authority or good reason, to have with him in a public place, any article which has a blade or is sharply pointed except for a folding pocket-knife which has a cutting edge to its blade not exceeding 3 inches." [CJA 1988 section 139(1)]