A new study has found that more than 80% of UK cities are vulnerable to urban heat, raising fresh concerns about how the country's built environment will cope with rising temperatures as climate change accelerates. The research highlights a growing risk facing urban populations across the UK, with implications that stretch from public health to energy demand and infrastructure planning. The findings underline what many climate scientists and urban planners have long warned: that Britain's towns and cities, many built decades or even centuries ago with little regard for extreme heat, are ill-equipped to handle the warming climate. Dense concentrations of concrete, asphalt and glass create what is commonly known as the "urban heat island" effect, where built-up areas retain and radiate heat far more intensely than surrounding rural land. With so many UK cities now flagged as vulnerable, the study suggests this is not a localised problem but a widespread structural challenge facing urban Britain as a whole. The implications for the energy sector are significant. As summers grow hotter and heatwaves become more frequent, demand for cooling is expected to rise sharply, placing additional strain on the electricity grid at a time when the UK is already navigating the complex transition to net zero. Air conditioning and other cooling technologies, historically less common in British homes and offices compared with hotter climates, may become increasingly necessary, adding a new dimension to national energy demand planning that has traditionally focused on winter heating loads rather than summer cooling. This shift also has knock-on effects for how the UK approaches renewable energy deployment and grid resilience. A future in which cooling demand spikes during heatwaves, potentially coinciding with periods of reduced wind generation, would require careful management of energy storage and flexible generation capacity. It reinforces the case for continued investment in battery storage, smart grid technologies and demand-side flexibility measures that can help balance supply and demand during periods of extreme weather. Beyond energy infrastructure, the vulnerability of UK cities to heat raises broader questions about urban design and adaptation. Green spaces, tree cover, reflective building materials and improved ventilation are among the measures often cited as ways to mitigate urban heat island effects, though implementing them at scale requires significant investment and long-term planning from local authorities and national government alike. The study adds to a growing body of evidence suggesting that climate adaptation must be treated with the same urgency as decarbonisation efforts. As the UK works towards its net zero targets, ensuring that cities can withstand the physical realities of a warming climate, including extreme heat, will be just as critical to protecting public health and maintaining a stable, resilient energy system in the decades ahead.