The U.K. is bracing for the hottest day on record on Monday with highs in the south of England.
Parts of central, northern, eastern and southeastern England were warned of a red extreme heat warning by the Met Office.
It is the first time in the country that such a warning has been given.
There are amber warnings in place for the rest of England, Wales, and parts of Scotland.
The U.K. Health Security Agency warned people in England to stay indoors and drink plenty of water.
The chances of a new high next week are 80%, according to the Met Office.
In Cambridge, eastern England, the temperature was 38.7C on July 25, 2019.
The capital is expected to be one of the hottest places on the planet on Monday.
The temperature in the city is expected to reach 40 degrees by Monday afternoon, making it the hottest city in the world.
The overnight temperatures are expected to be in the mid-twenties, before cooling on Wednesday.
Climate activists warn of rising global temperatures from greenhouse gases. Depending on global efforts to cut CO2 emissions, the world's average temperature is expected to rise by up to 4% by the end of the century.
The Met Office warns that the heat is set to have widespread impacts on people and infrastructure. Most of the homes in the U.K. don't have air conditioning.
Some schools plan to close early, or not open at all, and the country's main rail network has urged people to only travel "if absolutely necessary."
Retailers are expected to see a drop off in sales due to the hot weather and shoppers opting to stay indoors.
Retail footfall and travel will be affected by the heat in the U.K., with many shoppers choosing to stay at home and not go out in the heat.
It is a challenging time for businesses because of the twin pressures of high inflation and a cost-of-living crisis.
The impact of the heatwave on the U.K. economy is likely to be minimal given the precedent for people to work from home.
The U.K. economy grew by a small amount in May.