Geothermal in Cornwall
Although they are a long way from any volcanic areas, Cornwall and west Devon have a vast source of geothermal energy; granite. It is heat-producing, which means that the rocks here are hotter than anywhere else in the UK, making this the best place to exploit geothermal energy for both heat and power.
GeoScience has promoted the use of geothermal energy for power and heat in Cornwall since the 1980s.
UK Heat flow map - BGS
Granite outcrops in red