I tend just to round any fare up to the nearest pound, this is not a tip per se, but just convinent for me and a bonus for them)
However, upon returning home from a night out in Liverpool recently, when I rounded up a fare from £14.50 to £15, my mate got all indignant and insisted on giving the driver a few quid. Apparently my "tip" was insulting.
Any thoughts on this? Who was right? Does cab etiquette vary regionally?