Yes. There are fairly tight criteria on what are allowed, mind: manual opening short blades with no serations that don't lock open and (I think) don't have fing

Yes. There are fairly tight criteria on what are allowed, mind: manual opening short blades with no serations that don't lock open and (I think) don't have finger guards are ok. Most Swiss Army knives are fine, most Gerbers and Crkts aren't. Mora's and other fixed blades are right out. Edit to add: I carry an Opinel no 8, which is technically illegal on two fronts, but would be utterly impractical as a weapon. I've only ever had one problem doing so: one got confiscated at security going on the Millennium Wheel about a decade ago, but there was no other comeback from that and they're dirt cheap, so I just bought another.