The Met Office said a new provisional record temperature of 40.3C was recorded in Coningsby, in central England, with 29 sites across the country experiencing temperatures in excess of the previous high of 38.7C recorded in 2019.
Stephen Belcher at the Met Office said he had not expected to see such temperatures in the UK in his career.
“Research conducted here at the Met Office has demonstrated that it’s virtually impossible for the UK to experience 40C in an undisrupted climate but climate change driven by greenhouse gases has made these extreme temperatures possible,” he said.
Train services on major routes from London up the east and west coast of the country were cancelled, electricity companies reported mass outages and normally busy city centres appeared quiet.
Network Rail tweeted a number of pictures showing large bends and kinks in rail tracks.
London Fire Brigade declared a major incident and urged people to stop having barbecues as hundreds of firefighters battled blazes across the capital.
To the east, a large fire engulfed homes in the village of Wennington, with flames tearing across about 40 hectares of neighbouring tinder-dry fields.
Elsewhere large grassland areas around the capital caught fire, billowing smoke over major roads and nearby areas.
London’s Ambulance Service said it had been dealing with 400 calls an hour because of the extreme heat.
“We are seeing an increase in the number of patients experiencing heat exposure, breathing difficulties, dizziness and fainting,” said Peter Rhodes, the deputy director of ambulance operations.
The UK, which can struggle to maintain key transport services in extreme heat or snow, had been put on a state of national emergency over the unprecedented temperatures.
“My thanks go to all the firefighters and frontline services who are working incredibly hard to keep us safe on this scorching day,” Prime Minister Boris Johnson said on Twitter.
Transport minister Grant Shapps said there had been a considerable amount of travel disruption.
“Infrastructure, much of which was built from the Victorian times, just wasn’t built to withstand this type of temperature,” he said.
Operator Network Rail advised passengers to only travel if absolutely necessary.
“Extreme Heat: All services stopped. Do not come to the station,” Avanti West Coast, which runs services from London to cities such as Liverpool, Manchester and Glasgow, said on Twitter.
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