The hottest day on record last summer resulted in 638 more deaths in England than normal, according to official figures, which experts said show the danger that extreme heat and climate change pose to human life. The following day, when temperatures remained almost as high, 496 more people died than would usually be expected. The sudden spike in deaths on 19 and 20 July 2022, when temperatures rose above 40C (104F) for the first time on record, was revealed by the Office for National Statistics in data detailing daily deaths. The extra death toll is higher than had been predicted by experts at the London School of Tropical Hygiene and Medicine (LSTHM). With temperatures barely dropping below 27C at night, doctors warned that dehydration, overheating, heat exhaustion and heatstroke could be fatal, particularly for infants, old people, the homeless, outdoor workers and those with pre-existing medical conditions. Over the two days, there were 3,805 deaths across England from all causes, up 42% on the five-year average of 2,671. At least six people died getting into trouble in water, but the largest number of deaths was expected to be among the elderly, particularly those aged 85 and over. The UK Health and Security Agency has previously estimated that a later prolonged heatwave from 8 to 17 August saw an estimated 1,458 excess deaths, excluding Covid-19, in those over 65. Age UK said the figures should be “a wake-up call for all of us”. Caroline Abrahams, the charity’s director, said: “As we get older, our bodies find it harder to manage extremes of heat as well as cold, so as the planet warms and we seek to adapt our lifestyles, as well as reduce carbon emissions, this is something that planners, builders and the NHS all need to take increasingly into account.” Hundreds of firefighters battled blazes across England as temperatures recorded at RAF Coningsby in Lincolnshire surged to a high of 40.3C – a full 1.6C higher than the previous high, set in 2019. “There is an absolutely huge spike on each of these two days,” said Prof Sir David Spiegelhalter, chair of the Winton centre for risk and evidence communication at the University of Cambridge. “Deaths due to cold tend to be much more diffuse over time. Heat can kill more suddenly. These excess deaths are just because of the heat because the spike is so clear. It is rare to get a spike like that unless there is a massive accident. It is extraordinary data and shows the harm of extreme heat.” The environment and health modelling lab at LSTHM had estimated the excess deaths would total 966 over four days. The government declared a level 4 heat alert, meaning “Illness and death may occur among the fit and healthy, and not just in high-risk groups”.