Actually I almost always carry a knife in the form of a multitool, guess I'm used to it from trekking. Strange world that a man can no longer carry the tool of tools.
It is perfectly legal to carry a knife as a tool .

And unless you have some Chuck Norris style roundhouse kicks up your sleeve, then the person with the knife will have a big advantage when it comes to attacking you.
No offence* Caledonian but on this subject experience wise have you any idea what you are talking about ?(*no offence because getting through life without too many dodgy events and having to do nasty things to people isn't a bad thing at all)