To the east, a large fire engulfed homes in the village of Wennington, with flames tearing across about 40 hectares (100 acres) 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.
Britain, 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 front line services who are working incredibly hard to keep us safe on this scorching day,” Prime Minister Boris Johnson said on Twitter.
'DO NOT TRAVEL'
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.
Climate scientists said the once-unthinkable temperature in London was likely to become more common in coming years.
Sony Kapoor, a climate and macroeconomic professor at European University Institute, said he had long thought that people underestimated the physical impacts of climate change in contemporary times. “But even I never thought we would see 40 degree Celsius in London in 2022,” he said.
The arrival of a searing heatwave that first sparked wildfires across Europe before arriving in Britain has turned the spotlight on to “net zero” pledges made by the candidates running to replace Boris Johnson as prime minister.
After Johnson championed the move to net zero status when Britain held the United Nations COP26 climate change summit in 2021, some of the candidates to replace him have appeared more lukewarm and rated other challenges facing the country as their priority.
After Tuesday's heat, the Met Office said the temperature would fall on Wednesday, however it warned there could be heavy thunderstorms.