The temperature has hit 39.1C (102.4F) in Charlwood, Surrey – a new all-time UK record.
Charlwood is a village in the Mole Valley district of Surrey, about 4 miles from Gatwick Airport.
The previous record was 38.7C (101.7F), set in 2019 at Cambridge Botanic Garden.
Temperatures as high as 41C (105.8F) are forecast today, with much of England still under the first ever red weather warning.
The night-time record was broken overnight, as Kenley in Surrey hit 25.8C (78.4F).
UK currently hotter than 98.8% of the planet – heatwave latest
Keep out of the sun between 11am and 3pm and avoid physical exertion
Drink plenty of fluids and avoid excess alcohol
Close curtains in rooms that face the sun
Never leave anyone in a parked car – and check in on elderly and vulnerable neighbours
Walk in the shade, apply sunscreen and wear a wide-brimmed hat
Check medicines can be stored according to instructions – and check that your fridges, freezers and fans are working properly
And while the UK didn’t see a new record on Monday, Wales did see a new high mark as temperatures hit 37.1C (98.8F) at Hawarden.
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The sweltering heat has already caused significant travel disruption, with Luton Airport forced to suspend flights on Monday because of a defect in the runway.
Find out the five-day forecast where you live
Much of England remains under the Met Office’s first ever red warning as the country’s historic heatwave emergency continues amid stark warnings that we are seeing climate change in action.
Trains cancelled and routes closed due to hot weather
Rail users have been warned of delays and cancellations as the heat takes its toll on the country’s infrastructure, while health worries remain amid the baking temperatures.
There will be no Thameslink or Great Northern trains running in any location north of London, from London Blackfriars via St Pancras, or from London King’s Cross or London Moorgate.
Merseyrail said the number of trains running and journey times will be “seriously affected” and some routes closed completely.
LNER will run no trains from south of York and south of Leeds to London King’s Cross.
Southern, Southeastern, South Western Railway and Great Western Railway are among the dozens of train companies running significantly reduced services across the country.
Transport for London (TfL) said London’s rail network would also be running a reduced service due to safety restrictions put into place to deal with the heat.
‘A pretty unprecedented day’
Rachel Ayers, a Met Office forecaster, says Tuesday will be “a pretty unprecedented day”, with the mercury possibly reaching highs of 41C (105.8F) in spots in England.
“This will make it the hottest day on record and the first time we have seen temperatures as high as 40C,” she said.
Scotland and Wales could also see their hottest days on record.
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While Monday did not see a new UK heat record set – it was the third hottest ever – Wales did see a new high mark as temperatures hit 37.1C (98.8F) at Hawarden.
The potential for chaos on Britain’s roads and rails remains, with the public urged not to travel unless “absolutely necessary”.
Ms Ayers added: “There are likely to be delays on roads, with road closures, as well as possible delays and cancellations to trains and maybe issues with air travel.
“This could pose a significant health risk to those stuck on services or roads during the heat.”
A national emergency was declared last week amid the threat of severe disruption as schools close, hospitals cancel appointments and events are scrapped.
Council gritters – awoken from their summer hibernation early – are on stand-by to spread a light dusting of sand on melting roads.
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‘We are now a hot country’
Heatwaves like the one we are experiencing this week will “repeat themselves and get more severe going forward in time”, climate change expert Sir David King told Sky News.
Bob Ward, policy director at the Grantham Research Institute on Climate Change, told Sky News that the UK “has got to stop thinking of itself as a cold country”.
“In the summer months, we are now a hot country,” he said.
“There is no excuse for the government’s lack of preparedness for this kind of extreme heat event.”
Boy, 14, missing and four others have died
The dangers of extreme temperatures were laid bare once again in tragic fashion, with at least four people losing their lives during the heatwave.
A 14-year-old boy is also missing and believed to have drowned after getting into difficulty in the River Thames in London on the hottest day of the year.
Emergency services have issued urgent appeals for people to stay out of dangerous waterways and reservoirs.
Net-zero ‘never been more important’
As the country roasts in the baking heat, the issue of the government’s commitment to achieving net-zero has been under scrutiny amid the Tory leadership race.
All four remaining candidates have now publicly backed net-zero, following an apparent U-turn by Kemi Badenoch when questioned by COP26 chief Alok Sharma on Monday.
Mr Sharma has threatened to quit if the new prime minister ditches the current commitment to reach net-zero carbon emissions by 2050.
Prince Charles has also stressed the necessity of net-zero in light of the heatwave, saying it has “never been more vitally important”.
The outgoing PM Boris Johnson will discuss the heatwave at his last scheduled cabinet meeting today, having been criticised for skipping a COBRA summit over the weekend as he planned his farewell party.
