Huge reserves of energy have been found in rocks far below the surface of the ground in Britain. It is estimated that the north and southwest regions could hold enough energy in the form of heat to provide power for millions of homes. In fact, up to a fifth of Britain's energy could be provided by this geothermal source. Extracting the heat and converting it into electricity is difficult and expensive. 

Thousands of bore holes would be needed; but once they were in place, the heat would keep regenerating indefinitely.