Britain has recorded its hottest June day on record, shattering the previous high, which has stood since 1976.
The record broke four times on Wednesday, with 36.1C being recorded in Gosport, Hampshire, the Met Office said.
This came after 36C was recorded in Gosport and also in Wisley, Surrey.
Meanwhile, 35.8C was recorded in Wiggonholt, West Sussex, and 35.7C in Charlwood, Surrey.
This unprecedented heat surpasses the previous record of 35.6C, which had stood since 1976 and 1957.
The record-breaking temperatures arrived as much of England and Wales endured exceptionally hot and humid conditions, prompting a rare red warning for extreme heat from the Met Office.
Forecasters suggested that the figures could climb further, with more records potentially being broken in the coming days.
This intense heatwave, which has already triggered health warnings, school closures, and significant transport disruption, is being driven by a “heat-dome” that is currently settled over western Europe, bringing extreme conditions across the continent.
Experts warn that the collapse of the 50-year-old record is a stark illustration of climate change, which is primarily fuelled by the burning of fossil fuels. This is leading to increasingly frequent and intense heatwaves, for which the UK is reportedly unprepared.
Figures are currently provisional, and will be verified at the end of the heatwave to check whether they constitute a new national record.
Met Office science manager Amy Doherty said: “If confirmed, a new June daily temperature record would be significant, especially following on the heels of the recent records set in May.
“The new record provides further evidence that temperatures previously considered extreme are becoming increasingly common as a result of human-induced climate change.”
Temperatures could rise even higher on Thursday, the Met Office said.
If they hit 39C, that would make it the second-hottest day in the UK on record, and the hottest June day on record. If 38C is recorded, that is still in the top five days ever recorded and hotter than any day in the 20th century.
The record comes amid a sweltering heatwave, with the Met Office issuing a rare red warning for extreme heat for Wednesday and Thursday, covering areas from London and the south coast to Swansea, Somerset and Birmingham.
Red heat health alerts have also been issued by the UK Health Security Agency (UKHSA) for the east of England, the East Midlands, London, the South East, the South West and the West Midlands, and amber heat health alerts for the North East, the North West, and Yorkshire and the Humber.
These alerts will be in place from 1am on Wednesday to 11pm on Thursday, and mean that “adverse temperatures are likely to impact on the health and wellbeing of the population”.
The Met Office has also issued an amber warning for heat on Friday, covering much of England, while a yellow warning for thunderstorms is in place for the South West on Thursday evening.
And with the extreme heat set to linger in some parts of the country into the weekend, the Met Office has issued an amber warning for extreme heat covering parts of east and southeast England on Saturday.
At least 1,000 schools and nurseries will either be closed or partially closed in England and Wales over the next two days.
Some have brought in early finishing times or relaxed uniform rules, while transport services have been disrupted and people are being urged to stay inside, close windows and curtains, and stay hydrated to beat the heat.
Night-time temperatures have also been unusually high, staying above 20C in many places, with Brize Norton in Oxfordshire not dipping below 22.3C and Heathrow, west London, not dipping below 22.1C, the Met Office said.
These “tropical nights” make it hard to sleep and for people to recover from the heat of the day, experts warned.
More than 100 schools will be at least partly closed in Bristol, Gloucestershire, Oxfordshire, Buckinghamshire and Hampshire. In Somerset, more than 200 schools will be shut or have limited opening hours.
Children at some schools have been told they can wear PE kit rather than full school uniform, which can involve long trousers and blazers.
Education secretary Bridget Phillipson said that parents should send children to school if the school remains open, adding that schools are taking steps to help pupils cope with the heat, and that absences have a cost.
“I know hot weather can be a struggle. But my message to families is simple: if your child’s school is open, you should keep sending them in to school,” she said.
Transport bosses have urged people to avoid travelling on Wednesday and Thursday, and are warning those who do to “prepare for a disrupted journey”.
Travel into central London in the past few days was down on last week, as workers heeded advice to stay at home during the heatwave, while there were disruptions on a raft of rail lines.
The heatwave has prompted new calls for the government to take more action to protect the UK from increasingly extreme heat – a feature of the changing climate – including measures to cool hospitals, schools and care homes.
The Met Office said the frequency and intensity of heatwaves has increased worldwide.
Professor Stephen Belcher, Met Office chief scientist, said: “Human-induced climate change has made events like this more likely and more intense.
“To see temperatures like this in the UK in June is sobering.
“Events like this bring home the implications of climate change, with very high temperatures and humidity bringing significant health implications from heat stress, as well as impacts to a range of sectors such as transport, energy and water supply.”
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