The United Kingdom's meteorological agency, the Met Office, has released a provisional assessment that shows that the temperature exceeded 25º C overnight in several regions of the country for the first time since records began.
According to Met Office meteorologist Rachel Ayers, Tuesday's highs will reach "unprecedented" levels.
“The temperature will be very hot throughout the day and will rise to 40º C or even 41º C in isolated spots in England this afternoon,” she said.
The United Kingdom is experiencing hot and dry weather similar to what continental Europe experienced last week and which caused fires in many countries.
A large part of England, from London to Manchester and Leeds is under the country's first "extreme heat" warning.
On Monday, the temperature reached 38.1º C in Santon Downham, in the east of England, just below the highest temperature ever recorded in the UK - 38.7º C, a record set in 2019.
Average July temperatures in the UK range from 21°C during the day to 12°C at night, so few homes and almost none of the small businesses have air conditioning.
Many Brits are coping with the heat wave by staying at home, so road traffic has dropped dramatically.
London's Kings Cross station, one of the country's busiest rail hubs, was empty this morning with no trains from the busy east coast line, which links the capital to the north and Scotland.
London's Luton airport had to close its runway because of heat damage.
British Transport Secretary Grant Shapps explained that the UK's transport infrastructure, some of which date back to Victorian times, "just weren't built to withstand this kind of temperature" - and replacing it will take "many years".