The trouble is the government and police have done such a good job scaring the crap out of the sheeple over guns, knives etc, the chances of being nicked for carrying anything are high. You could use an anke type sheath if you have long leg jeans on say, or the best place for a knife is a low/mid back sheath along your spine, point up handle down, and theres also the kevlar or plastic xray defeating knife, not much use for sawing or chopping etc just for combat.
The average joe would shop you in a heartbeat if they thought you had anything on you...
I personaly carry a Stanley folding lock knife available from b&q.
http://www.stanleytools.co.uk/product/147149
now whether I'd get away with carrying it if I were stopped who knows but it is a D.I.Y. knife so......
Also other tool companys do them such a s hilka etc...
"Some say the end is near, some say we will see Armageddon soon...
I certainly hope we will, I sure could use a vacation from this silly shit."