An environmental charity said the country is "clearly unprepared for rising extreme temperatures" and called on the Government to tackle the increasing health threats posed by heatwaves.
UK Health Security Agency figures show 33 heat-related deaths took place in Devon, Cornwall and the Isles of Scilly during the four heat episodes of summer 2024, which corresponds to 18 deaths per million population.
Meanwhile, 1,311 such deaths were registered across England over the same period, including 282 more than anticipated, based on the observed temperatures during the summer and the historic temperature-mortality relationship in the country.
The UKHSA health alerting system identifies, categorises, and communicates when adverse temperatures are likely to impact the health and wellbeing of the population.
A yellow heat-health alert is issued when a period of heat is unlikely to impact most people, but could affect those who are particularly vulnerable, while a more serious amber alert is issued when wider impacts are expected, with potential for the whole population to be at risk.
A heat episode takes place when the UKHSA issues an amber warning in at least one region, or when the mean Central England Temperature reaches at least 20 degrees Celsius.
Four episodes met this definition in 2024, comprising a total of 14 days – the fourth lowest number of days since records began in 2016.
The higher-than-anticipated number of deaths in three of the four heat episodes came despite relatively cooler conditions, which prompted only yellow heat-health alerts from the UKHSA.
A total of 467 heat-associated deaths were registered during the second heat episode which took place between July 18 and 20, for instance.
Older people were more at risk during last summer's heat episode, with 521 deaths per million people aged 85 years and over, and 111 per million people aged 75 to 84 years.
Sophie O’Connell, senior policy adviser at Green Alliance, said the number of heat-related deaths across England last summer shows the country is "clearly unprepared for rising extreme temperatures".
She warned "climate change exacerbates existing health inequalities", but insisted "the health impacts of climate change, like extreme heat, are avoidable".
She added focusing efforts on protecting those who are disproportionately affected by heatwaves, including vulnerable and elder people, "can bring multiple benefits" and is key to support the population against extreme weather conditions.
"If the Government is serious about creating an NHS fit for the future, these figures are a clear warning: it must act now to tackle the rising health risks of heatwaves," she said.
Danny Gross, climate campaigner at Friends of the Earth, said these figures are "tragic evidence of the lethal impacts of climate breakdown", and called on the Government to tackle rising extreme weather threats.
He said: "The Government's upcoming climate plan will be a litmus test of how serious it is about preventing future heat deaths.
"The plan must enable the UK to hit its legally binding climate targets, while also delivering cheaper energy bills, better public transport and more green jobs.
"Ministers must also do more to protect people across the country from the growing threat posed by extreme weather events, such as heatwaves and floods, by strengthening the Government's woefully inadequate national adaptation programme."
Dr Agostinho Sousa, head of extreme events and health protection at UKHSA, warned "periods of heat in the UK are likely to become more intense, longer and more frequent as the world continues to warm", adding there is a "need for a coordinated health response even during less intense periods of heat".
He said the UKHSA continues to work to protect those most likely to be affected by extreme weather conditions.