The Met Office has issued an amber extreme heat warning with temperatures forecast to hit the high 30s this week and into the weekend.
The amber grading, which covers much of the southern half of England as well as parts of eastern Wales, will be in force from Thursday through until the end of Sunday.
Temperatures are expected to peak on Friday and Saturday, with highs of up to 36C.
A temperature of 40.3C was recorded at Coningsby in Lincolnshire on 19 July, the Met Office said, as the nation sweltered.
The record was broken three times in a few hours with 39.1C measured in Charlwood, Surrey and 40.2C at Heathrow Airport.
Scientists have warned that the extreme heat is fuelled by climate change, which is making heatwaves more intense and frequent.
What is an amber weather warning?
The Met Office issues weather warnings when severe weather has the potential to affect health, power supplies, travel and water availability. The warnings are given a colour - yellow, amber or red - depending on a combination of both the impact the weather may have and the likelihood of the impacts occurring.
An amber warning is issued when there is an increased likelihood of severe weather affecting day-to-day lives. This means there is the possibility of travel delays, road and rail closures, power cuts and a potential risk to life.
This could be through floods, storms, or extreme heat.
The Met Office advises that people think about changing plans and taking action to protect themselves if an amber warning is in place. It issued the amber alert on Monday as part of an extreme heat warning based on consecutive days exceeding average temperatures across the country.
Watch: UK Weather Forecast London To Swelter On ‘Hottest Day Of Year’ Amid Heatwave Health Warning
Met Office Deputy Chief Meteorologist Dan Rudman said: “Thanks to persistent high pressure over the UK, temperatures will be rising day-on-day through this week and an extreme heat warning has been issued.
“Temperatures are expected to peak at 35C on Friday and Saturday, or even an isolated 36C on Saturday. Elsewhere will see temperatures widely into the high 20s and low 30s Celsius.
“Coupled with the high daytime temperatures there will be some warm nights, with temperatures expected not to drop below the low 20s Celsius for some areas in the south.”
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How dangerous is it?
An amber weather warning indicates a risk to life if not prepared for and dealt with appropriately.
Dr Agostinho Sousa, head of Extreme Events and Health Protection at the UK Health Security Agency (UKHSA), said: “Heat-health alerts have now been issued to the majority of the country, with temperatures set to remain consistently high throughout the duration of this week.
“Most of us can enjoy the hot weather when it arrives, but it is important to keep yourself hydrated and to find shade where possible when UV rays are strongest, between 11am and 3pm.
“If you have vulnerable family, friends and neighbours, make sure they are aware of how they can keep themselves protected from the warm weather.’’