A potentially transformative energy source lies directly beneath the United Kingdom, and it is not the ghost of King Coal. Recent assessments by the British Geological Survey and private developers have revealed that deep geothermal reservoirs, drilled to depths of 4 to 5 kilometres, could provide a significant fraction of the nation’s electricity and heating needs. Unlike wind or solar, geothermal energy delivers baseload power — reliable, continuous, and independent of weather conditions. The implications for energy security and net-zero targets are profound.
Geothermal energy works by tapping into the Earth’s internal heat. Water is injected into hot, permeable rocks deep underground, heated by the surrounding geology, and then pumped to the surface to drive turbines or supply district heating networks. The UK’s geothermal potential has been known for decades, but high upfront costs and uncertain resource mapping stalled development. Now, advancements in drilling technology, borrowed from the oil and gas industry, have reduced costs dramatically. Horizontal drilling and hydraulic stimulation, techniques perfected in shale fields, allow access to larger volumes of hot rock from a single well.
New data from the United Downs Deep Geothermal Power project in Cornwall, the first deep geothermal electricity plant in the UK, confirms that temperatures of 190°C can be reached at 5 kilometres depth. This is well above the threshold for electricity generation. The plant, operated by Geothermal Engineering Limited, is expected to generate 3 MW of electricity and 20 MW of thermal heat, enough to power 3,000 homes. The company plans to drill a further 10 wells in the region by 2026, creating a cluster that could supply 50 MW of baseload electricity.
The geothermal resource is not confined to Cornwall. The Cheshire Basin, the Weald basin, and parts of Northern Ireland and Scotland all show promise. Granite basement rocks, which are naturally fractured and contain radioactive elements that generate heat, are abundant beneath the UK. The British Geological Survey estimates that harnessing just 10% of the accessible geothermal heat could provide 20% of the UK’s electricity demand by 2050. For heating, which accounts for roughly 30% of UK energy consumption, the potential is even greater. Deep geothermal wells can feed district heating networks, replacing natural gas boilers in densely populated areas. Southampton already uses a geothermal well for district heating, and new projects in Gateshead and East London are under development.
Critically, geothermal energy is sovereign. The fuel is the Earth itself, and the drilling rigs can be operated by British companies using British steel. This eliminates exposure to volatile global fossil fuel markets, a lesson painfully learned during the 2022 energy crisis. The levelised cost of electricity from new geothermal plants is falling rapidly, currently estimated at between £50 and £80 per MWh, competitive with onshore wind and solar, but without the need for backup storage.
However, hurdles remain. Upfront capital costs are high, typically £20 million to £30 million per deep well. And drilling outcomes are uncertain: not every site yields sufficient heat or flow rates. The government’s recent Energy Security Bill includes provisions for a geothermal support scheme, but campaigners argue it is too modest. A geothermal accelerator akin to the successful offshore wind contracts for difference could unlock private investment and drive down costs.
The environmental footprint is minimal. Geothermal plants emit virtually no carbon dioxide during operation; any greenhouse gases released from the deep Earth are orders of magnitude smaller than those from fossil fuel combustion. Land use is compact a single well pad can power tens of thousands of homes. There are risks of induced seismicity, but these are manageable with careful monitoring, as demonstrated by thousands of geothermal plants in Iceland, the United States, and France.
A crucial advantage is that geothermal infrastructure can be retrofitted to existing oil and gas wells that have reached the end of their productive lives. The UK has tens of thousands of such wells, and repurposing them could cut development costs in half. This gives the fossil fuel industry a direct incentive to pivot to clean energy.
The time for dithering is past. As the Arctic sea ice shrinks and heatwaves intensify, the imperative to decarbonise is absolute. Geothermal energy offers a proven, scalable, and reliable path to a zero-carbon grid. The heat is there, beneath our feet. All that is missing is the will to drill.
