The UK is basking in its hottest June day in 41 years, with a temperature of 34.5 C( 94 F) recorded at Heathrow.
The Met Office reading at the London airport is the highest in June since the mercury reached 35.6( 96 F) in 1976 – the all-time high since records began.
The heatwave has ensure five sizzling days in a row during which temperatures in parts of the UK have topped 30 C.
But weather warns have also been issued for rain, with thunderstorms expected in some areas.
BBC weather presenter Chris Fawkes said: “To have these really prolonged spells, you need a block of high pressure that directs other climate fronts away.
Then we get the hot weather coming up from Europe.”
Storms are forecast for some areas later in the day, and yellow weather warns for rain in parts of England, Wales and Scotland are in place until the early hours of Thursday.
Our presenter added: “It is all going to go bang tonight.
“The hot air from the surface will meet with colder air coming in from the Atlantic and we will have some big thunderstorms, gusty gusts, heavy rain and, in some places, even hail.
Summer of 1976
The record-breaking summertime of 1976 saw nine weeks of blazing sunshine.
Between June and August, blue skies were a daily occurrence and, for two weeks, temperatures were 32 C or above consistently.
Five days considered temperatures outstrip 35 C.
The hottest day of all was 3 July, with temperatures reaching 35.9 C in Cheltenham.
A downside was the worst drought in recorded history for the UK, building up from a warm summertime in 1975 and unbelievably dry months after.
Rainfall in the winter of 1975 was half of what it normally would be, and by the summer of 1976 crops were affected and there were forest fires in the south of England.
But once the summer had come to a close, autumn ensure intense rainfall and natural balance was restored.
The crowd heading to Royal Ascot were hoping for a similar relaxation of dress code to the one race-goers experienced on Tuesday.
Normally humen attending the horse racing event in the Royal Enclosure must wear black or grey morning dress with a waistcoat, tie and a top hat.
But the jacket regulation was not enforced for the first time in its history, as organisers took a “common sense approach”.
Whilst some are taking to the parks or the beach to lap up the sunshine, people on the daily commute have been faced with traveling interruption.
Greater Anglia Trains has cancelled a number of its services between London and Essex, telling the heat has led to velocity restrictions on the lines to stop them from buckling.
For those in more congested areas, the Department for Environment and Rural Affairs has also alerted there may be pockets of high pollution during the exceptionally hot weather, especially in the East Midlands.
Emergency services have warned people to keep safe in open water after three people died in separate incidents around the country.
A 15 -year-old boy died after get into difficulty when swimming in a pond with friends in Walsall, West Midlands.
This follows the deaths of a adolescent who drowned in a reservoir near Rochdale and an elderly woman who rescue teams tried to save off the coast of Sussex.
A West Midlands Ambulance Service spokesman said: “Although it is very hot at the moment, the dangers of going into open water cannot be underestimated.”