At least 2,700 people are estimated to have died from heat-related causes in England and Wales during May and June’s record heatwaves, researchers say, as UK health officials prepare their official assessment in coming weeks

The figure comes from researchers at Imperial College London, the Met Office (Britain’s national weather service) and the London School of Hygiene and Tropical Medicine (LSHTM), based on established data on the health risks of extreme heat.

Most of the deaths are believed to have occurred during the June heatwave, which made it the hottest June ever recorded in England. Temperatures reached 37.7C at Lingwood, Norfolk, breaking the previous June record of 35.6C, set in 1957 and equalled in 1976.

During those days, authorities issued a rare red heatwave warning for parts of England and Wales, cautioning that even healthy people faced a serious risk to their health.

May also brought record-breaking temperatures, with the UK reaching 35.1C at Kew Gardens on 26 May, a sharp rise on the previous record of 32.8C, set in 1922 and equalled in 1944.

Scientists attribute both heatwaves to a heat dome: a large, stationary zone of high pressure that trapped hot air over the region for days on end. Human-induced climate change is understood to have made the effect worse, having warmed the planet by around 1.4C since pre-industrial times. Researchers estimate this warming added between 3 and 4C to the peak temperatures recorded in May and June.

Unusually warm overnight conditions, known as tropical nights, added to the discomfort by giving little relief from the daytime heat. Much of the UK’s housing stock was not built to withstand such conditions, leaving many people especially exposed to prolonged high temperatures.

Extended exposure to heat puts significant strain on the body, an effect worsened by dehydration as the heart works harder to keep the body cool. Babies, older adults and people with existing health conditions face the greatest danger, with extreme heat capable of triggering heart attacks, strokes and other life-threatening emergencies.

Heat exhaustion typically brings on dizziness, heavy sweating, clammy skin, nausea and muscle cramps. Heatstroke is more serious and can involve confusion, a lack of sweating despite a body temperature above 40C, hot and dry skin, nausea, and in severe cases loss of consciousness or seizures.

The study uses mortality data from previous years to model how many deaths are likely to have occurred in May and June 2026. Because it relies on assumptions about how badly people were affected by the heat, the findings have not been independently verified. The UK Health Security Agency (UKHSA) is expected to publish its own official estimate of heat-related deaths in the coming weeks, based on national mortality records.

Dr Clair Barnes, a climate scientist at Imperial College London who worked on the study, said she hoped the figures would push people to take heatwave warnings seriously, adding: “These are big numbers and we don’t want to see this many people dying.”

Some of the researchers involved believe that, if current trends continue, heat-related deaths in parts of northern Europe could begin to approach the number linked to cold within the next couple of decades. They stress this outcome would depend heavily on how quickly global emissions are cut and how well countries adapt to rising temperatures.

Heatwaves are expected to become more frequent, more intense and longer-lasting as greenhouse gas emissions continue to rise, scientists say.