COMMUTERS were sweltering on packed trains in "journeys from hell" today as Britain was heating up for a 40C "hottest day ever" scorcher.
The mercury is expected to soar to an "unprecedented" 40C, smashing the current record of 38.5C set in Kent in August 2003.
Brits in London and the south-east were urged not to travel unless absolutely necessary as speed restrictions due to the heat sparked delays and cancelled trains.
Commuters needing to get to work were forced to endure slow journeys on packed, boiling trains. By 7am, it was already 25C at Kenley Airfield.
The hot weather is blasting in from an African plume of Saharan air.
Some forecast models show the high humidity levels could make the temperature feel like 44C today.
The dangers of cooling off in lakes, rivers and the sea were highlighted by emergency services after the bodies of three people were pulled from the water after they reportedly got into difficulty swimming.
Searches continue for someone seen in the River Thames near Waterloo, Scotland Yard said.
The scorching conditions may spark thunderstorms which could trigger travel delays, flash flooding, and power cuts, the Met Office said.
A yellow weather warning is in force for most of England, except the south west, and parts of Scotland from 3pm on Thursday until 4am on Friday.
Overnight lightning storms have already caused fires and rail disruption this week during the heatwave.
Yesterday, the Met Office said the temperature hit 33.7C at Cavendish in Suffolk and reached 33.5C in Writtle, Essex.
At Heathrow in London, the mercury rose to 32.4C, while at St James's Park it reached 31.9C.
'STAY AT HOME'
The sweltering conditions prompted Network Rail to impose train speed restrictions in areas where tracks were at risk of buckling.
Southeastern railway even urged commuters to avoid travelling, as services were expected to experience huge delays.
Extreme weather action teams (EWATs) were "activated" to keep passengers safe and trains running.
Now emergency services warned the public to take precautions during the extreme heat.
Temperatures reached 35.5C on the Central Line yesterday.
Commuters were snapped appearing rather worse for wear, on packed tubes.
Officials have also highlighted the risks of cooling off in the sea, lakes and rivers.
The Rail Delivery Group, which represents the industry, advised passengers in London and the South East to change their travel plans on Thursday because of the expected heat.
Met Office Meteorologist Matthew Box said it is more likely both the 36.7C July record and the all-time maximum of 38.5C will fall before the end of the week.
He said: “We now think there is an 80-per cent chance that the July record will be broken on Thursday with a 40-per cent chance the all-time record will fall.
“Models indicate a lot of warm air coming up from the Continent especially across eastern parts of the country.
“High pressure is over the Continent and this allowing energy from the sun to heat the region, this air is then going to come up and into the UK.
“There is a chance that it will turn slightly fresher as we go into the weekend, however eastern Britain could remain very warm.”
As temperatures soar across the country, emergency services warned the public to take precautions during the extreme heat and highlighted the risks of cooling off in the sea, lakes and rivers.
MELTING ROADS
And gritters could be brought out during the heatwave as temperatures could cause roads to melt.
RAC Breakdown spokesman Rod Dennis said: “The sweltering heat is going to inevitably lead to some softer road surfaces over the next few days.
“If you see some blacker patches of road or pavement, that’s how you can tell it’s starting to melt.
“It also means that drivers might start to see something that they’d normally only associate with the depths of winter – gritting trucks.
“Salt can help improve the grip on roads that are starting to melt.”
Meanwhile, people across the country have been sharing their reactions to the weather - and not everyone's loving it...
MORE THUNDER
The hottest day ever comes a year to the day after The Sun told how the planet was gripped by a mammoth killer heatwave, with temps hitting 35C in Britain.
Experts at the Energy & Climate Intelligence Unit last night warned of the potential impact of today's forecast record temperature.
Deputy director Peter Chalkley said: “Exactly a year to the day since The Sun’s iconic ‘world’s on fire’ frontpage, Britain could see its all-time temperature record broken.
“In the past year the Met Office has told us that 2018’s heatwave was made around 30 times more likely by climate change.
“Scientists have predicted and tracked the increased frequency and severity of heatwaves and the British public are increasingly concerned about climate change.
“Experts are highlighting that older people and also the very young as well as farmers and even power stations can struggle in the increased heat we are seeing.”
It comes after lightning storms triggered fires and rail disruption on Tuesday night.
Incredible pictures captured the skies illuminated with arcs of lightning as powerful electrical storms.
The Met Office last night issued a yellow warning for scattered thunderstorms covering the east of the country from Scotland down to London from 3pm on Thursday and into early Friday morning.
It also warned flooding and lightning strikes could affect driving conditions, disrupt train services and lead to power cuts.
Record-breaking temperatures are also expected across Europe.
The most extreme heat will now build from central and northern France into Belgium, Netherlands, Luxembourg and far western Germany into Thursday.
Temperatures of 40.6C are forecast for Paris, breaking the current record of 40.4C at Parc Montsouris, set more than 70 years ago.
We pay for your stories! Do you have a story for The Sun Online news team? Email us at [email protected] or call 0207 782 4368 . You can WhatsApp us on 07810 791 502. We pay for videos too. Click here to upload yours.