Researchers estimate that more than 2,700 people in the UK may have died from heat-related causes during exceptionally hot weather in May and June, according to modelling by teams at Imperial College London, the Met Office and the London School of Hygiene and Tropical Medicine. Most of these deaths are thought to have occurred during the June heatwave — the warmest June on record in England — when a rare red heat alert warned even healthy people of a significant risk to life. The findings underline how extreme heat, often described as a "silent killer", poses a growing threat in a country whose homes and infrastructure are largely not built to cope with prolonged high temperatures.

Both heatwaves were driven by a "heat dome" — a stalled area of high pressure that trapped hot air over the region — which researchers say was worsened by human-induced climate change estimated to have added between 3 and 4C to peak temperatures. June saw 37.7C recorded at Lingwood, Norfolk, while May reached a new UK high of 35.1C at Kew Gardens, far above previous records. The estimates are modelled from past death records and carry uncertainty; notably, 2025 saw roughly half the predicted deaths, which experts attribute partly to heat health alerts and NHS action. Scientists warn that heatwaves are likely to become more frequent, intense and longer-lasting as greenhouse gas emissions continue, with some suggesting heat-related deaths in northern Europe could eventually rival cold-related ones.