[stikypad]

220 VAC allows higher gauge (thinner) wires for the same wattage consumption and more watts per circuit for the same amperage (more powerful appliances and/or more concurrent appliances without tripping a breaker). And the UK in particular has far safer plugs than the US, with a fuse in every plug, partially insulated plug leads, and blocking shutters on the sockets.

So basically we could use less copper, have safer homes, and simplify power supply design since we (and a handful of other holdouts) are basically the only countries using 100-120 VAC rather than 210-230 VAC, which would lower costs and reduce waste.