Thousands of people could die in the coming heatwave, experts have warned, as the government triggered the first ever national emergency heat red alert with a record 40C (104F) temperature forecast for south-east England on Tuesday. Health officials fear people living alone on upper floors of buildings are among those who could perish, as people did in Paris in 2003. Last year two lesser heat episodes caused about 1,600 excess deaths, according to official figures. The level 4 heat alert announced for Monday and Tuesday by the UK Health Security Agency (UKHSA) means “illness and death may occur among the fit and healthy, and not just in high-risk groups”. The Met Office described the forecast heat that is coming from France and Spain as “absolutely unprecedented” and urged people to treat it like a storm warning and consider changing plans. Operations are being cancelled in parts of the NHS, some schools are closing early or shutting altogether and Network Rail advised people not to use trains that will be slowed down amid fears of buckled rails. Record night-time temperatures of more than 25C (77F) in London and parts of the north-west are also forecast, placing greater strain on people’s bodies for longer, a key factor in increasing mortality. “We could see 1,500 to 2,000 deaths just from this one period of heat,” said Bob Ward, the policy director at the Grantham Research Institute on Climate Change and the Environment. Prof Kevin McConway, emeritus professor of applied statistics at the Open University, said: “I think that, assuming the weather forecasts are roughly correct, it’s very likely that there will be hundreds or thousands of excess deaths from the heat in the next few days … It’s possible that, because there have been so many warnings about the coming high temperatures, people and businesses will be taking more precautions than usually happen in a heatwave, which could lower the numbers of excess deaths. I hope that happens, but I fear there will still be excess death on quite a scale.” Public health officials are urging people to stay indoors with curtains closed and to avoid caffeine and alcohol and physical exertion in the hottest parts of the day. “Here in the UK we’re used to treating a hot spell as a chance to go and play in the sun,” said Penny Endersby, the Met Office chief executive. “This is not that sort of weather.” The UKHSA said to “look out for those who may struggle to keep themselves cool and hydrated – older people, those with underlying conditions and those who live alone are particularly at risk”. Climate scientists said temperatures of 40C had been predicted for the UK in climate change modelling and warned the heatwave would increase pressure on the next prime minister to improve the UK’s resilience and come up with a better plan to cut greenhouse gas emissions. While temperatures are expected to fall later next week, in August a “heat dome” could develop over the Mediterranean that could also lead to very high temperatures being pushed north into the UK, forecasters said. The government’s Cobra emergency committee met on Thursday to discuss the heatwave and officials are to meet again over the weekend. “There is a range of contingency planning in place,” said a Downing Street spokesperson. This included speed restrictions on rail services, measures to ensure the safety of people who might have to queue in cars in roads or at ports, and more emergency hospital staff on duty. The announcement of a national heat emergency triggers “a multi‑sector response at national and regional levels”, according to the government’s heatwave plan for England. Concerns cited include risks to people in hospital; melting roads causing congestion and leaving people stranded in cars; railways buckling; and extreme heat on the London underground, as well as water shortages, smog, wildfires and risks to farm animals and pets. The Department for Digital, Culture, Media and Sport is also engaging with groups organising major events, such as the women’s Euro 2022 football tournament. But Labour alleged the government was “asleep at the wheel” and called for clear guidance for employers on safe indoor working temperatures, flexible working and more frequent breaks. The Met Office issued a parallel red “extreme heat warning” covering parts of central, northern, eastern and south-eastern England. The agency also extended amber warnings to cover Cornwall, west Wales and parts of southern Scotland. “Exceptional, perhaps record-breaking temperatures are likely early next week, quite widely across the red warning area on Monday, and focused a little more east and north on Tuesday,” said the chief Met Office meteorologist, Paul Gundersen. “Currently there is a 50% chance we could see temperatures top 40C and 80% we will see a new maximum temperature reached.” Network Rail has advised people to avoid rail travel across England and Wales on Monday and Tuesday and blanket speed restrictions across England and Wales are expected from 12-8pm on both days. London to York could take four hours instead of two, with trains forced to slow to below 60mph for safety. The RAC is expecting more than 1,000 extra daily breakdowns with the risk of car engines overheating or running out of fuel or coolants exacerbated by possible queues to reach beaches or the countryside. Relatives of care home residents have raised fears the heat could cause deaths, with many elderly people already in distress, “dripping with sweat”. The problem of soaring temperatures is being exacerbated by many care homes being in Covid lockdown, which limits visitors and means residents are asked to stay in their rooms, which are often not air-conditioned. Predictions of 40C were within the range of predictions in climate change models, said Prof Richard Betts, who leads on climate impacts at the University of Exeter and the Met Office Hadley Centre. “Climate change is making all heat events hotter,” he said. “The wind patterns would have happened anyway, but it is happening against the background of hotter conditions because of climate change.” Asked if it could be a one-off, he said: “We are already seeing more frequent, longer and hotter heatwaves. We can confidently attribute this to human-caused climate change. We can expect this to keep happening until we reduce global greenhouse gas emission to net zero.”