The UK has experienced its hottest June day on record after temperatures soared to 36.1C (97F) in Gosport, Hampshire on Wednesday afternoon.
Hundreds of schools shut across England and Wales and transport has also been disrupted, with train passengers advised to avoid all non-essential travel.
The heatwave is forecast to continue into Thursday and Friday, with a further high of about 38C possible, the Met Office said.
A red extreme heat warning issued by the Met Office across parts of south and central England and south Wales remains in place until 23:59 BST on Thursday.
The high for the day came between 15:00 and 16:00 BST – breaking the previous June record of 35.6C recorded in Southampton in 1976 and Camden in 1957.
This new record is described as “provisional” by the Met Office, which now has to conduct checks to ensure the measurement is reliable.
The next highest temperatures of the day were all recorded in southern England, including Wisley, Surrey on 36C, Wiggonholt, West Sussex on 35.9C, and Charlwood. Surrey on 35.7C. And Wales had its hottest day of the year so far, with a high of 33.3C at Cardiff Bute Park.
Meanwhile, a searing European heatwave continues to cause deaths and disruption, – with France recording its hottest day since records began in 1947, and the temperature in Paris and other areas above 40C.