A new assessment from His Majesty’s Treasury has confirmed what geophysicists have long suspected: the granite batholiths beneath Cornwall and the deep sedimentary basins of the North Sea hold enough geothermal energy to power British industry for centuries. The report, circulated to cabinet ministers this morning, characterises the resource as “transformative” and suggests that levellised costs could undercut offshore wind by 2030.
For decades, geothermal has been the quiet cousin of renewables. While solar and wind captured headlines and subsidies, the heat beneath our feet was dismissed as a niche technology, viable only in volcanically active regions such as Iceland or Kenya. But recent advances in horizontal drilling and closed-loop heat exchange, borrowed directly from shale gas extraction, have changed the calculus. The Treasury’s analysis models a scenario in which deep geothermal provides 50 GW of baseload capacity by 2040. That is roughly half the UK’s current electricity demand.
The physics is straightforward. Below 5 kilometres, rock temperatures exceed 150 degrees Celsius. Circulate water through a sealed system of fractures and you bring that heat to the surface. Flash it to steam and drive a turbine. No carbon dioxide. No intermittency. No dependency on weather patterns. The Earth’s internal heat flux is a nuclear reactor wrapped in stone, and we are finally learning how to tap it.
The Treasury’s enthusiasm stems from two specific variables. First, the geological endowment. The Cornubian batholith, a 250-million-year-old granite intrusion extending from Cornwall to Devon, is exceptionally hot and permeable. The East Yorkshire basin, meanwhile, offers deep saline aquifers at pressures ideal for binary cycle plants. Second, the declining cost curve. Drilling costs have fallen by 40 per cent since 2015, driven by technology transfer from the oil and gas sector. The Treasury estimates a capital expenditure of £8 million per MW installed, comparable to onshore wind.
For British industry, the implications are profound. High-temperature process heat is the single largest source of industrial emissions. Cement, steel, chemicals and glass require sustained temperatures that solar cannot provide and biomass struggles to maintain. Geothermal offers a direct thermal substitute: pipe hot brine from 5,000 metres straight into a factory’s steam network. The Treasury calculates that a single deep geothermal well could supply a major chemical plant with heat for 40 years.
There are, of course, barriers. The initial exploration risk remains high. Drilling a 6-kilometre well costs £15 million and there is no guarantee of sufficient permeability. The Treasury proposes a ‘geothermal insurance’ fund under the UK Infrastructure Bank, absorbing the geological risk so that private capital can follow. Regulation also needs updating: the current licensing framework treats geothermal as mining, not energy. A dedicated Geothermal Act, expected in the next King’s Speech, would streamline permits and grant access to the seabed for offshore projects.
The environmental community is broadly supportive, though concerns exist about induced seismicity. The British Geological Survey has monitored small seismic events associated with geothermal stimulation in Cornwall, none exceeding magnitude 2.0. Closed-loop systems, which never contact the rock directly, eliminate this risk entirely. Several start-ups are now piloting fully sealed ‘coaxial’ heat exchangers that require no fracturing.
The clock is ticking. Every month of delay means another 20 million tonnes of CO2 from industrial gas burners. The Treasury’s language is unusually direct: “This is not a long-term option. It is an immediate opportunity.” The Granite beneath our feet is not benevolent or malevolent. It simply is. But it holds energy, and that energy can replace carbon. That is the only calculation that matters.
