Updates from Thursday 25 July 2019
UK has hottest July day on record, with 38.1C recorded at Cambridge
"Heat-related incidents" cause train delays and cancellations across UK
Europe is also experiencing the heatwave, with Paris reaching 40.6C
Network Rail warns of disruption where tracks are at risk of buckling
Forecasters say the heat could lead to downpours in some areas
The Met Office has about 270 weather measuring stations across the UK feeding back hourly updates.
You can see where they all are here, external.
It is the in the south and east of England where temperatures are expected to be the highest today, peaking at a record 39C.
Members of the Southern Counties Petanque Association have been enjoying the sunshine and promoting the sport at Southampton's urban beach.
It's one of the events at the Seaside in the Square attraction which has brought a sandy beach to Guildhall Square in central Southampton.
Also known as French Boules, the sport has an enthusiastic following in the UK and there was a campaign to have the sport included in the 2024 Olympics.
Duncan Leatherdale
BBC News Online
If you think it is hot in the UK, spare a thought for our friends on the continent.
A red alert has been issued in Northern France - with temperatures of 41C forecast in Paris.
Image source, Getty ImagesFrench officials have warned people to avoid travelling, and to work from home if possible. Children's nurseries have also been closed.
The chief architect responsible for restoring the Notre-Dame has warned that the extreme heat could lead to the cathedral roof collapsing if the joints and masonry holding up the roof dry up.
Belgian, German and Dutch temperature records could be broken for the second time in two days.
Lisa Constable in Oxfordshire is putting her feet up to enjoy her day off.
We're not jealous at all ☀️
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Hold on to your hats! Lord's Cricket Ground has relaxed its rules on members having to wear jackets for the test match between England and Ireland.
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BBC Breakfast
St John's Ambulance's medical director, Dr Lynn Thomas gave us some advice on how to spot dehydration.
She also shared these first aid tips, external for hot weather problems like heatstroke and fainting.
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Duncan Leatherdale
BBC News Online
I asked for pictures of dogs and you have not disappointed (in the interests of fairness and balance I should stress pictures of other animals are also welcome).
Jason Selman snapped these great shots of his dogs Syd and Elsie cooling off in Swanage, Dorset.
Image source, Jason Selman
Image source, Jason Selman
Image source, Jason SelmanBy 10:00 the temperature had already climbed above 30C (86F) in some parts of London, the Met Office said.
Heathrow Airport has recorded a temperature of 31.6C (88.88F) and Kew Gardens, west London, has already seen the mercury hit 31.7C (89.06F).
Rob England
BBC England Data Unit
As you get your dose of vitamin D in today's sunshine, make sure you have some sun cream to hand to protect your skin.
The NHS says, external there is no safe way to get a tan and you can burn even when it's cloudy.
Here's a few helpful tips:
Chris Waring
BBC News
No, this isn't the music video for an 80s power ballad...
Reporters at BBC East Midlands are making use of a giant fan to cool down.
On what could be the hottest day of the year, temperatures in Nottingham could rise above 34C (93F) today.
Do you want to see how hot your day will be?
Click here to find the weather for wherever you are.
Below is how the rest of the day looks in Birmingham.
Dan French from Greater London is 34 today but the heatwave has scuppered his plans.
Happy Birthday from us Dan - stay cool however you choose to celebrate.
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Image source, Dan French
Sandish Shoker
BBC News
East Midlands Trains has warned there could be disruption to some services today and timetables have been amended as trains go slower to prevent rails from buckling under the heat.
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On a day that could see record-breaking temperatures in the UK, BBC Weather Watchers in the east of England have already been out and about - presumably before it gets too hot!
"Ebb&flow" found a dog walker in Hinxton, Cambridgeshire, had heeded advice to walk pets early in the morning, posting this image at 06:15.
Image source, Ebb&flowA Weather Watcher in Graveley, Hertfordshire, found farm workers were also threshing the fields early doors to make the most of slightly cooler weather.
Image source, Weather WatcherMeanwhile, user "Daves Patch" in Holme-next-the-Sea in Norfolk captured horses getting some early exercise.
Image source, Daves PatchThe car is the last place we want to be today. But some of us dedicated people have places to be.
Drivers are sharing pictures of their dashboards to show how hot it is already.
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It's a debate that divides office-dwellers across the nation - is it ever ok to wear shorts to work? This is BBC weather presenter Simon King's answer...
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Jessica Labhart
BBC News
Hundreds of students and their families are gathering for some sunny graduation ceremonies in Birmingham.
Victoria Square and the ICC seem to be popular places for a quick photo before the big day.
The Metro is reminding passengers how to stay cool during today's scorching commute.
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Duncan Leatherdale
BBC News Online
Our friends at CBBC have created this fun quiz about extreme weather.
I scored a measly two out of seven, go ahead and put me to shame.
While extreme weather events like heatwaves occur naturally, "research shows that with climate change they are likely to become more common, perhaps occurring as regularly as every other year, external", the Met Office says.
It conducted a study last year that found that the UK was now 30 times more likely to experience heatwaves compared to the year 1750, because of "the higher concentration of carbon dioxide (a greenhouse gas) in the atmosphere".
Records going back to the late 19th Century show that the average temperature of the Earth's surface has increased by about one degree since industrialisation.
What's causing the heatwave?
A climatology institute in Potsdam, Germany, says Europe's five hottest summers since 1500 have all been in the 21st Century.
Scientists are concerned that rapid warming linked to use of fossil fuels has serious implications for the stability of the planet's climate.