Britain's electricity grid needs replacing. Our old power network is approaching obsolesence. That means that there's a real threat of a new army of pylons spreading out across some of our most beautiful landscapes.

Since the advent of electricity, power cables have spread out from large, centrally-located coal-fired power stations. In the future we're going to be extracting our power from small sources dotted around the periphery of the country- wind, wave and hydro-electric stations far from the big power users of the major cities. To cope with this change a new national grid will have to be constructed. The shape of that grid and the method for transferring power is already provoking controversy. How acceptable are large pylons in our National Parks? How much more expensive is an underground cable? Tom Heap investigates the options.