If I lived in a less peaceful place, I'd carry a knife. Unfortunately, the British Government plasters anybody carrying a knife as a hoodlum and a murderer, so God help you if you trip and your knife falls out of your pocket. That's a surefire way to get arrested. Naturally, people with nothing to lose have no such reservations about carrying weapons, and so you should have the right to carry something to protect yourself.
I live in the middle of a big city. Literally, the middle. Fortunately, any trouble is alcohol-induced, and you rarely need a weapon to fight a drunk.