If I catch someones eye I usually smile and say hi or something else. I personally enjoy when people smile at me, so hey why not.
Never smile at people on the street.... if you do, they might turn into an angry hellhound-wildebeast and eat your soul for breakfast. Instead, walk in a straight and narrow line down the street, never making eye contact with anyone. Be afraid and concerned with every human that approaches and give them a wide berth. This is the time tested, media approved method for breeding new generations of american idiots. .... and I'm sure it would work in England too.