A few years ago they dug up our road. They dug up every road in town. They dug up pretty much every road in the UK. "They" were cable TV companies, and they were installing fibre-optic cables. The roadworks caused gridlock - and as demand for digital communications grows, we'll need more cables, and they'll be digging up the roads again. Demand for information-carrying capacity, or bandwidth, is always likely to exceed supply, because the more capacity there is, the more ways we will think of to use it. High-definition TV, high-definition DVDs, video phones, video-on-demand downloaded to your computer. Robotic vacuum cleaners controlled over the internet. Three-dimensional TV...

There is another way. Every home in the developed world already has an older system of cables, installed to carry electrical power. Why can't we make power cables carry additional signals? Electricity is transmitted at high voltages, unlike digital signals, but ...