An amber heat-health alert has been issued for much of England, with temperatures expected to rise above 30C (86F) over the weekend.
The alert, issued by the UK Health Security Agency (UKHSA), covers London, the East Midlands, and the south-west, south-east and east of England.
It is due to come into force at midday on Friday and will remain in place until 6pm on Tuesday. A yellow alert has also been issued for Yorkshire and the Humber, and the West Midlands.
The UKHSA warned that the prolonged heat could have a significant impact on health and social care services.
It follows a previous amber alert issued on 19 June, when temperatures hit 32.2C in Kew, west London, prompting official heatwave declarations across England and Wales.
The latest warnings come as parts of eastern England are forecast to reach 27C on Thursday, with thunderstorms possible in the south and east as a result of lingering warm, humid air.
The Met Office meteorologist Honor Criswick said: “For the first part of the day, it is set to be unsettled, [with] outbreaks of quite heavy rain at times, particularly across Scotland.
“But it’s fairly fast moving, so by the time we reach the afternoon, particularly from the west, we’re going to see the return of those bright and sunny spells.
“And behind this area of rain, a much fresher feel to the air as well.”
Temperatures are expected to climb again before the weekend, with highs of up to 28C in southern and eastern parts of the country expected by Friday, while western regions may have some heavy rain, and the east could remain dry with sunny spells.
But Criswick warned that “low pressure is never too far behind”, with “some rain on the cards to finish off the week and as we head into the weekend”.
Scientists say the climate crisis is making heatwaves more frequent and intense, especially during the early part of summer.
