The Met Office has announced the record for the hottest June day has been broken for a second day in a row.
A provisional temperature of 36.4C was recorded in Yeovilton, Somerset, surpassing the high of 36.1C set on Wednesday in Gosport, Hampshire.
It comes as the forecaster has extended its red warning, currently in place for a swathe of England and Wales, until 9pm on Friday for London and parts of east and south-east England, stretching across Oxfordshire and Bedfordshire, Hampshire and Kent, because of the exceptional heat and humidity.
Temperatures could exceed 36C in these areas, perhaps rising to 38C in some places, the Met Office said.
As the Met Office extended its red warning for extreme heat to 9pm on Friday for London and parts of south eastern England, chief meteorologist Andy Page said: "This exceptional spell of hot and humid weather will maintain its grip on the UK for a little longer.
"Although the current red warning for areas in more central and western parts of England and Wales will expire later today, the heatwave will still be bringing high temperatures to these areas, albeit moving away from the peak heat of Wednesday and Thursday.
"We are expecting that some daytime maximum temperatures could exceed 36C, perhaps rising to 37C in some locations."
There will also be high humidity, which would lead to uncomfortably warm, humid nights, the Met Office said.
The heat will continue to rise across England
|PA
Meanwhile, Sir Keir Starmer said schools have to decide for themselves whether it is right to close early as a result of the heatwave.
Asked if it was right that children’s education suffer because of the extreme weather, the Prime Minister said: "It is very hot, and obviously schools will have to take the appropriate measures, and each school will gage for themselves the measures that are appropriate.
"But it is important that we as a Government co-ordinate this across the country, and actually with all of the countries within the United Kingdom, which is what we’re doing."
Cobra meetings are taking place "at the official level", Sir Keir said, adding: "Obviously it falls to me and others to say, take care, be sensible with precautions, and schools are going to have to decide. They are deciding."
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Multiple weather alerts are in place across England and Wales
|MET OFFICE
In the capital, the London Ambulance Service has recorded its highest ever number of life-threatening emergencies as temperatures soared across the south.
Ambulance crews responded to a record 642 Category 1 calls, including the most serious, life-threatening injuries and illnesses such as cardiac arrests and patients who are not breathing.
Chief Executive Jason Killens KAM said: "We have seen the highest number of life-threatening emergencies in our history, driven by the extreme heat across London.
"Our crews are working very hard in challenging conditions to care for patients, and I would like to take this opportunity to thank all our people for their incredible hard work. Please help them to help you by taking care of yourself and others – stay out of the sun and keep hydrated."
The London Ambulance Service responded to a record number of calls
|REUTERS
South East Water have announced a temporary hosepipe ban for people living in Kent amid the heatwave gripping the UK.
A spokesman for the company said: "Due to high temperatures and record demand for water across Kent, a Temporary Use Ban (hosepipe ban) is now in place for customers in our Kent supply area.”
"Demand for drinking water in South East Water’s Kent supply area has reached very high levels in June, driven by the latest heatwave to impact the region.
"To ensure that the company can provide a consistent public water service for all its customers in the county, South East Water is moving to restrict the use of hosepipes and sprinklers with immediate effect."