The temperature has hit 40.2C (104.3F) at Heathrow Airport – a new all-time UK record.
Earlier today, 39.1C (102.3F) was recorded in Charlwood, Surrey – breaking the previous record of 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), while Kew Gardens and Heathrow surpassed the previous temperature record by noon on Tuesday, recording temperatures of 38.8C (101.8F).
UK currently hotter than 98.8% of the planet – heatwave latest
How to stay safe in the heat – official advice
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
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.
On Tuesday, police said a section of a dual carriageway in Cambridgeshire was left looking like a “skatepark” after it warped in the heat.
Find out the five-day forecast where you live
Rail users have been warned of delays and cancellations as the heat takes its toll on the country’s infrastructure.
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, said Tuesday will be “a pretty unprecedented day”, with temperatures possibly reaching highs of 41C (105.8F) in spots in England.
Scotland and Wales could also see their hottest days on record.
This is now officially the most extreme heatwave on record in the UK.
The warmest-ever night has been followed by the warmest-ever day.
And temperatures will continue to climb for several more hours.
While the blistering heat is just uncomfortable for most, for some it can be serious.
The NHS is seeing a spike in 999 calls as people struggle with heat exhaustion or worse.
Sadly there will be deaths directly related to the temperature too.
Heatwaves are becoming more intense and more frequent as a result of climate change.
Temperatures of 40C are unprecedented now.
But by the end of the century, the Met Office predicts they’ll be reached every decade or so.
The damage from heat, storms and flooding will rise sharply as climate change accelerates – and so will the costs.
Not just in repairs, but also in the adaptation that will become more and more pressing.
Our infrastructure and buildings are just not built for the heat we are experiencing now, let alone in the future.
And the longer it takes to reach net zero, the more extreme the weather will be in the future.
Wavering on our climate commitments would end up costing us all more.
Explainer: Heat exhaustion and heatstroke – what are the signs and symptoms and what’s the difference?
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.”