Since records began, only four days have been hotter than today in the UK.
The highest temperature ever recorded was on 19 July 2022 when temperatures at Coningsby, Lincolnshire, reached 40.3C. That marked the first and only day that readings above 40C have been seen in the UK.
Before that, the record was 38.7C at Cambridge Botanic Gardens on 25 July 2019.
Faversham in Kent reached 38.5C on 10 August 2003, while on 18 July 2022 a temperature of 38.2C occurred at Pitsford, Northamptonshire.
Amber warnings for “extreme heat” are in place for a swathe of England from London to Sheffield, parts of Cheshire and Greater Manchester, into Gloucestershire and Wiltshire in the South West and Shropshire and Herefordshire in the west.
Temperatures were also forecast reach 35C in Wales, where a drought has been declared across the whole country.
Meanwhile, a yellow thunderstorm warning is in place for Northern Ireland until 06:00 on Friday, while rain is forecast for much of Scotland.
In England, the extreme heat in this heatwave is now believed to have peaked, with cooler temperatures of 30-34C expected for the Midlands, East Anglia and much of southern England by Friday, ceding to 26C by Sunday.
More than 27 million people are facing water use restrictions, including hosepipe bans.