Official figures revealed a spike in the number fatalities as the June temperatures approached the 30 degree mark.
The Office for National Statistics said 259 more deaths than average had coincided with weather that triggered a heatwave alert from Public Health England. The figure contrasts with a period immediately before the hot weather took hold, in which 214 fewer deaths than the five-year average for the same period had been recorded.
A high of 30.1C was recorded in London on June 25, making it the UK’s hottest day of the year so far at that point.
Maximum temperatures exceeded 24.5C until the end of June – above the level at which the Government warns that heat-related deaths may occur.
During that period, there were 382 more deaths in England than the average for the same period between 2013 to 2017.
A peak and fall in the number of deaths was also recorded in April, the same figures show, coinciding with another spell of hot weather. There were 243 more deaths between April 18 and 19 than the five-year average across the same period, and 378 fewer between April 21 and 23.
Bob Ward, policy and communications director of the Grantham Research Institute on Climate Change and the Environment at the London School of Economics, said the design of buildings was a factor in the list of casualties.
He said: “It is likely that many of the people who died during the hot weather suffered from underlying illnesses, such as respiratory disease.
“Nonetheless, many of these deaths may have been prevented if buildings were better adapted to prevent overheating.
“The Government has been warned by experts for a number of years that the awareness of the public needed to be raised about the increasing risks of heatwaves due to climate change.
“This summer was the warmest on record in England, and analysis by the Met Office shows that the incidence of heatwave conditions is rising.”
Mr Ward has previously criticised ministers for “shockingly poor” communication with the public about the effects of heatwaves.
The temperature of homes, workplaces, trains and hospitals is not currently regulated by law, and there is no official upper limit on temperatures permissible in classrooms.
The Commons Environmental Audit Committee, has warned that heat-related deaths in Britain will more than triple to 7,000 a year by 2050 and has said the Government had failed to appreciate the dangers.
Its chairman, the Wakefield MP Mary Creagh, said in July: “Heatwave warnings are welcomed as barbecue alerts but they threaten health, wellbeing and productivity.”
She said the Government must “develop a strategy to protect our ageing population from this increasing risk”.
Annie Campbell, at the Office for National Statistics, said: “Although the provisional data currently available appears to show a high number of deaths at the end of June, we can’t confirm the heatwave is the cause.”