The UK's most extreme heatwave coincided with a surge in temperature-related deaths in a “stark warning” of the effects of climate change, new figures revealed on Friday.

England's hottest days of 2022 were linked to an estimated 4,507 deaths, the Office for National Statistics said, the highest annual figure on record.

The average yearly figure since 1988 had been closer to 1,400 but analysts say there are signs heat-related deaths are increasing.

The UK recorded its first ever 40ºC day during a heatwave that peaked on July 19, 2022. Forecasters warn it may happen every three years by 2100 due to climate change.

The alarming trend is believed to put Londoners specifically in the firing line because of the urban “heat island” effect, which heightens health risks in cities.

Homes in Britain are built for mild temperatures and air conditioning is not commonplace. Dying from cold used to be far more common than heat but the gap has narrowed in recent years.

Antonio Gasparrini, an epidemiologist at the London School of Hygiene and Tropical Medicine who worked on the ONS report, told The National the rise in heat deaths was not surprising given the growing frequency of heatwaves.

“This is a stark warning that this will become the norm due to climate change, and it makes even more urgent the need to implement adequate climate and public health measures,” he said.

He said there was little point hoping for a compensating drop in cold-related deaths in warmer winters, since scientists would expect the rise in heat deaths to be “far steeper”.

A climate adaptation plan published by ministers in July warned of an economic hit due to workers becoming overheated in future. But Prime Minister Rishi Sunak announced on Wednesday that the UK would delay key net-zero targets, in what was widely seen as a pre-election gamble.

“It is quite telling that this report comes out just days after the UK government has decided to dilute their commitment on net zero and generally on policies to reduce greenhouse gas emissions,” Prof Gasparrini said.

The deaths in England in 2022 “were associated with the hottest days”, statisticians said. They added that “any change in climate towards more extreme temperatures would likely lead to an increase in attributable deaths”.

“Historically, very low temperatures were responsible for a greater number of deaths than very high temperatures, although over recent years there is some indication that heat-related deaths have increased,” said Gillian Flower, an ONS climate and health analyst.

“We continue to develop our methods to measure climate-related health outcomes, and monitor the situation in the context of the increasing frequency of hotter days.”

Britain coping with heat through the years – in pictures

A further finding was that the risk of heat-related death is higher in London than in other parts of England or Wales. In the capital, the danger is three times greater once temperatures go above 29ºC than in optimal weather, according to the data series from 1988 to 2022.

Statisticians are not sure why this is but believe it could relate to London’s demographic profile or urban character, an ONS spokeswoman told The National. Cities can be warmer due to a lack of trees as well as cars and buildings emitting warmth due to the “heat island” effect. Fires broke out across London during the 2022 heatwave.

“London usually experiences higher summer temperatures than other places, in addition to the phenomenon of heat island effect in higher densely-populated and urbanised areas, which can increase personal exposure to heat even further,” Prof Gasparrini said.

The new figures control for wind speed, humidity, seasonality and days of the week, but there are “other factors that may impact temperature-related mortality we have not been able to include so far” and “part of our aim for this analysis is to highlight areas that warrant further investigation”, the ONS spokeswoman said.

All regions of England and Wales showed an increased risk of death above 22ºC, with those aged over 65 the most vulnerable.