Britain was braced for temperatures to hit 40C for the first time this week, with ministers urging the public to stay at home as the heatwave caused train services to be cancelled, one London airport to shut its runway and some schools to close.
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.
Britain's government triggered a "national emergency" alert as temperatures were forecast to surpass the previous record of 38.7C (102F) in the Cambridge University Botanic Garden in 2019.
On Monday, the temperature nudged 38C in southern England and a new high was recorded in Wales, according to Britain's Meteorological Office. It is expected to be even hotter on Tuesday, when the 40C level is forecast to be exceeded.
"We've got a difficult 48 hours coming," Kit Malthouse, a minister in charge of government coordination, told BBC radio.
The heat brought widespread travel problems.
London's Luton Airport said flights were suspended after a surface defect was found on the runway, and the heat caused flights to be diverted from the Royal Air Force's Brize Norton air base.
The national rail network urged passengers not to travel unless necessary, with some services - including a key route between northeastern England and London - not running during parts of Tuesday.
London's metro network imposed temporary speed restrictions, meaning it would run a reduced service with journeys taking longer than normal.
Jake Kelly from Network Rail said he hoped normal operations would resume on Wednesday, when temperatures are forecast to fall, but that would depend on "the damage that the weather does to the infrastructure over the next couple of days".
To highlight the issue, Network Rail tweeted a picture of a rail with a kink near London.
HIGH ALERT
The government has urged schools to stay open but many were due to close earlier than usual, normal uniform demands were ditched and end-of-term sports days were cancelled. Some schools were shut, resorting to lockdown-style online lessons.
The public were warned not to swim in open water to cool off, with police reporting two teenagers had died after getting into trouble while swimming in a lake and a river.
Some factories also brought their opening hours forward, to prevent workers on the hottest jobs, such as welding, from falling ill.
At least one major zoo, at Chester, said it would close for two days, while in parliament, normal rules that require lawmakers to wear jackets or ties were eased.
Shopper numbers were down 7.3% across Britain compared to last week, according to researcher Springboard, although coastal towns saw a 9% increase as people flocked to the seaside.
The Health Security Agency (UKHSA) raised the heat health warning to Level 4 for England for Monday and Tuesday for the first time ever, while the Met Office issued its first ever extreme heat 'Red warning'.
A Level 4 alert is used when a heatwave "is so severe and/or prolonged that its effects extend outside the health and social care system. At this level, illness and death may occur among the fit and healthy, and not just in high-risk groups".
Heir to the throne Prince Charles said while on a trip to southwest England that the weather showed how vital it was that the country stick to its climate commitments.
"Those commitments around net zero have never been more vitally important as we all swelter under today’s alarming, record temperatures across Britain and Europe," he said.
"As I have tried to indicate for quite some time, the climate crisis really is a genuine emergency and tackling it is utterly essential," the long-time environmental campaigner said.
(Reporting by Kate Holton, Michael Holden, William James, and Farouq Suleiman; Editing by William Schomberg, Alex Richardson and Hugh Lawson)
