By Damian Carrington and Sarah Marsh From The Guardian UK

Nearly 700 more deaths than average were recorded during the 15-day peak of the heatwave in June and July in England and Wales, according to official statistics.

Experts said that an increase in deaths is fully expected during heatwaves, but they cautioned that the provisional data requires further analysis to determine if the higher mortality is statistically significant for the summer months.

“The heatwave will have been associated with a number of excess deaths,” said Dr Adrian Boyle of the Royal College of Emergency Medicine. “The people most at risk in a heatwave are the frail elderly with heart or kidney problems.”

The UK is “woefully unprepared” for deadly heatwaves, a cross-party committee of MPs concluded in a report published on 27 July. The MPs said the government had ignored warnings from its official climate change adviser, and that without action heat-related deaths will triple to 7,000 a year by the 2040s.

The height of the heatwave was from 25 June to 9 July, according to the Met Office, a run of 15 consecutive days with temperatures above 28C. The deaths registered during the weeks covering this period were 663 higher than the average for the same weeks over the previous five years, a Guardian analysis of data from the Office of National Statistics shows.

ONS analysis for previous years indicate hundreds of additional deaths were associated with brief periods of heatwave conditions in July 2016 and June 2017. The full toll of the 2018 heatwave could reach 1,000, according to one prediction.

“Although the 2018 data is only preliminary, there seems to have been a concerning increase in the number of deaths,” said Dr Isobel Braithwaite, of the public health charity, Medact. “This fits in with current scientific evidence, which clearly shows that long periods of very warm weather can harm people’s health, particularly at extremes of age and in people with other pre-existing health problems.”

“While working in A&E this summer, I saw patients presenting with heatstroke and other conditions that were probably exacerbated by the hot weather, and this obviously places an additional strain on our already struggling health services,” she said.

Saffron Cordery, deputy chief executive of NHS Providers, said: “Some trusts have reported record numbers of people coming in to A&E, with increased emergency admissions, often for respiratory problems and conditions made worse by dehydration. We have heard concerns about large numbers of people from care homes requiring treatment.”

Dr Nick Scriven, the president of the Society for Acute Medicine, which represents hospital doctors specialising in emergency care , said: “The pressure was real and felt at the frontline. I would not be surprised at all if an effect on mortality is shown. The figure of about 700 would seem very plausible.”

He said dehydration can lead to many issues, from dizziness and falls, to an increased risk of infections, heart attacks and strokes. High temperatures can increase air pollution, and some urban areas including London saw alerts issued for ozone pollution. “That can really affect those with respiratory conditions,” Scriven said.

The heat also puts NHS staff themselves under pressure, he said. “NHS staff are working in often intolerable conditions. Compounding the heat is the fact that this is prime holiday season and there is little slack in the system regarding staff numbers.”

Braithwaite said the 2018 heatwave showed that hospitals and care homes must be made ready to cope with high temperatures. “We now know that the frequency and intensity of heatwaves is set to increase significantly over the coming decades because of climate change, so we have to heed this warning call in order to protect the public’s health,” she said. “We also need to treat the underlying cause of the problem by rapidly cutting emissions.”

“The extreme heat has highlighted the shortcomings of ageing buildings, which are not designed or equipped to deal with these conditions,” said Cordery. “Staff and patients are paying the price now for past decisions to delay investment in the NHS estate.”

The ONS data records when deaths are registered, not when they occurred, but 77% of deaths are recorded within five days. Even higher levels of excess deaths are seen in the colder months, but the year-to-year variation is lower in the summer months.

“We cannot say whether any of these [663] deaths are due to the heatwave or from other causes,” said an ONS spokeswoman. “Causes of deaths data for 2018 will be published next summer and they may provide a better understanding.”