Britain could hit 40 Celsius (104 Fahrenheit) for the first time, forecasters said, causing havoc in a country unprepared for the onslaught of extreme heat that authorities said was putting lives at risk.
n London, the mercury was set to rise to highs of 38C on Monday as chief meteorologist Paul Davies warned there was a "good chance now of hitting 40C or 41C" on Tuesday.
"This is entirely consistent with climate change," he told Sky News, describing the "brutality" of the expected heat as "astounding".
Britain's current record temperature stands at 38.7 Celsius. Scientists blame climate change and predict more frequent and intense episodes of extreme weather.
Britain's government triggered a "national emergency" alert as temperatures were forecast to surpass the 38.7C (102F) recorded in the Cambridge University Botanic Garden in 2019 on Monday and Tuesday.
"We've got a difficult 48 hours coming," Kit Malthouse, a minister in charge of government coordination, told BBC radio.
London's metro network imposed temporary speed restrictions for Monday and Tuesday, meaning it would run a reduced service with journeys taking longer than normal. It urged commuters to only travel if essential.
Much of Europe is baking in a heatwave that has pushed temperatures into the mid-40s Celsius (over 110 Fahrenheit) in some regions, with wildfires raging across tinder-dry countryside in Portugal, Spain and France.
Across the Channel firefighters failed to contain two massive fires in France's southwest that have created apocalyptic scenes of destruction.
For six days, armies of firefighters and a fleet of waterbombing aircraft have struggled against blazes that have mobilised much of France's entire firefighting capacity.
Forecasters have put 15 French departments on the highest state of alert for extreme temperatures, including in the western Brittany region where the Atlantic coastal city of Brest was expected to hit 40 Celsius Monday, nearly twice its usual July temperature average.
The wildfires in France have forced more than 16,000 people, residents or tourists, to decamp. Seven emergency shelters have been set up for evacuees.
France's interior ministry announced it would send an extra three firefighting planes, 200 firefighters and more trucks.
"In some southwestern areas, it will be a heat apocalypse," meteorologist Francois Gourand told AFP.
Blazes burning in France, Greece, Portugal and Spain have destroyed thousands of hectares of land and forced thousands of residents and holidaymakers to flee.
The European heatwave, spreading north, is the second to engulf parts of the southwest of the continent within only weeks.
This report was produced with date sourced from Reuters and Agence France-Presse.