The temperature has exceeded 40C in the UK for the first time on record, with 40.2C reported at Heathrow at 12.50pm on Tuesday, according to provisional Met Office figures.
The threshold was hit at 12:50pm as much of the UK sweltered in a heatwave, with parts of England and Wales under a red warning for extreme heat, posing a danger to life, pressure on the NHS and disruption across transport networks.
It comes as the London Fire Brigade (LFB) declared a major incident due to “a huge surge” in blazes across the capital amid the 40C heat.
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Around 100 firefighters tackled a blaze in the village of Wennington, east London, on Tuesday afternoon, with television footage showing black smoke billowing into the air, with buildings and fields on fire.
The fire brigade said in a statement it was battling “several significant” incidents in the capital, as people have been urged not to have barbecues or bonfires due to the “unprecedented” challenges crews face.
London Mayor Sadiq Khan said the LFB was under “immense pressure”.
LFB’s assistant commissioner for operational resilience and control, Patrick Goulbourne, said: “The brigade remains ready to respond to incidents.
“However, we want to ensure our resources are available for people who really need our help.
“If you see a fire smouldering, please don’t hesitate to call us.
“The sooner we know about a fire, the sooner we can bring it under control and prevent it from spreading further, reducing the need for us to mobilise additional resources.
“We are also strongly urging people not to have barbecues or bonfires today as the ground is incredibly dry, which means even the smallest sparks could cause a fire.
“Please take care during the heatwave as all emergency services are facing unprecedented challenges.”
The 40.2C recorded at Heathrow beats the previous record for the UK of 38.7C in Cambridge three years ago, by 1.5C, and the Met Office warned temperatures were still climbing early on Tuesday afternoon.
Much of England and Wales are under a “red” extreme heat warning until the end of Tuesday, with the heat causing disruption on transport networks and the risk of serious health impacts.
It comes after UK experienced its warmest night on record on Monday as the extreme heat saw temperatures remaining in the mid-20s in some areas.
Charlwood, Wisley and Chertsey in Surrey, and Kew Gardens and Northolt in west London were among the places to exceed the 2019 record by early afternoon, with temperatures climbing above 39C.
Scotland and Wales could also see their hottest days on record today with temperatures set to rise cross the nation.
Brian Jordan, director of 999 operations for London Ambulance Service, said the service saw a slight increase in calls for fainting and heat exposure on Monday.
Transport Secretary Grant Shapps conceded the UK’s transport network cannot cope with the extreme heat.
He told people to “apply common sense” and “depending on the nature of your journey and reason for it you might want to consider rearranging your day around it”.
He told BBC Breakfast: “We’ve seen a considerable amount of travel disruption, we’re probably going to see the hottest day ever in the UK recorded today and infrastructure, much of it built in Victorian times, just wasn’t built to withstand this type of temperature – and it will be many years before we can replace infrastructure with the kind of infrastructure that could, because the temperatures are so extreme.”
Climate change is making heatwaves more extreme, frequent and likely, and experts warn the UK needs to adapt homes, hospitals, schools and transport networks to a future of more searing heat.
Much of Europe is also baking in record-breaking heat, which is fuelling wildfires in a number of countries.
Britons have been urged to stay inside during the hottest period of the day, between 11am and 4pm, and wear sun cream, a hat, stay in the shade and keep hydrated with water.