The UK could have its hottest day on record this week, with temperatures forecast to hit up to 41C (106F).
At 12:00 BST it was 34.8C in Charlwood, Surrey, making this the hottest day of the year so far after a morning of rapidly rising temperatures.
The Met Office has issued a red extreme heat warning on Monday and Tuesday in much of England, from London and the South East up to York and Manchester.
The current highest temperature in the UK is 38.7C, in Cambridge in 2019.
Temperatures above 34C have been recorded in London and Suffolk on Monday, with amber warnings in the rest of England, all of Wales, and parts of Scotland.
The capital is set to be one of the hottest places in the world, with temperatures soaring above the Western Sahara and the Caribbean.
Peak temperatures are expected on Tuesday afternoon, with Worksop, Nottinghamshire, forecast to see 41C by the Met Office.
It is the first time the Met Office has issued a red warning since the system was introduced last year.
It means “widespread impacts on people and infrastructure” are expected, with “substantial changes in working practices and daily routines” required.
Overnight temperatures warned to be in the mid-20s, before cooling on Wednesday.
Some schools plan to close early – or not open at all – although the government has issued guidance designed to keep them open.
LNER will not run services between London and Leeds and York for much of Tuesday.
Jake Kelly from Network Rail explained precautions are being taken to mitigate the impact of the extreme temperatures, but the heat would place railway infrastructure under “exceptional stress”.
Road congestion dropped by up to 10% in London, Birmingham, Bristol and Glasgow on Monday morning, compared with the same time last week, data from satellite navigation firm Tom Tom showed.
Responding to claims the UK has seen worse heat – such as during the prolonged heatwave in 1976 – BBC Weather’s Simon King said the expected temperatures are much hotter, up to 10C above the extended heatwave and severe drought experienced then.
“That is where you the real health impacts come into play because these are dangerously high temperatures.”
Alongside the Met Office’s red and amber warnings, the UK Health Security Agency has issued a level four warning for England, which the government is treating as a “national emergency”.
After an emergency Cobra meeting for ministers on Saturday, Health Secretary Steve Barclay said ambulance capacity would increase, alongside more call handlers.
Pressure on the NHS is also being felt over the impact of extreme heat on its infrastructure, which one senior leader described as being “quite dilapidated”.
Miriam Deakin, from NHS providers, told BBC Radio 4’s Today programme that some operating theatres are having to close because they cannot maintain required temperatures, as well as causing problems with IT servers.
Soaring temperatures are also having a devastating impact on much of Europe and north Africa, with authorities in western France warning of a “heat apocalypse” in 15 regions.
Wildfires have been wildfires raging from Greece to Morocco, with thousands being evacuated from and more than 1,000 deaths have been attributed to the heat in Portugal and Spain in recent days.
The heatwave is happening when average world temperatures have risen by just over 1C from their pre-industrial levels.
We are living in the hottest period for 125,000 years, according to the UN’s climate science body, the Intergovernmental Panel on Climate Change (IPCC).
We know what is behind this – greenhouse gas emissions caused by our burning of fossil fuels like coal and gas. Concentrations of carbon dioxide (CO2) in the atmosphere are at the highest level for two million years and rising, according to the IPCC.
If all the promises governments made at the UN COP26 climate conference in Glasgow last year are actually implemented then we’re looking at temperatures rising by 2.4C by the end of the century.
But the bad news is that emissions of CO2 continue to increase. Without big cuts by 2030 we could see temperatures go even higher. Perhaps as much as 4C by the end of the century, scientists predict.
What does that mean? I think you know the answer to that. It means more frequent and intense heatwaves like this.
Read more here.
Sunday was the hottest day of the year so far with temperatures reaching 33C in Flintshire, 32C in Cheshire, 27.7C in Armagh in Northern Ireland, and 26.4C at Auchincruive in Ayrshire.
Water companies in southern and eastern England have warned increased demand is leading to low pressure – and even interrupted supply – for some households.
Experts have urged people to drink water, keep their curtains closed where possible, and to check on friends and relatives.
“In this country we’re used to treating a hot spell as a chance to go and play in in the sun,” said Prof Penny Endersby, Met Office chief executive. “This is not that sort of weather.”
While there is no warning in place for Northern Ireland, temperatures are predicted to reach 30C on Monday.