The unprecedented temperature of 29.3 degrees Celsius (84.7 degrees Fahrenheit) was recorded at the famous botanical park Kew Gardens in southwest London.
The previous record of 27.4C (81.3F) was set in 1990 in the coastal town of Lossiemouth in northern Scotland.
This May 1 is also the hottest day of the year so far in the country.
Like other European countries, the UK has been experiencing a heatwave since the beginning of the week.
According to early estimates from the Met Office, April was the sunniest since meteorological records began in 1910.
It was also the third warmest, with an average temperature of 9.6C (49.2F) – 1.7C above the long-term average.
“The sun is as strong as it usually is in August,” said Met meteorologist Aidan McGivern.
The high temperatures and dry conditions have led to numerous fires across the country.
On Thursday, a fire broke out in West Yorkshire in northern England, adding to the more than 400 fires recorded in the country so far this year, according to the National Fire Chiefs Council.
That number is significantly higher than in previous years.
Over a hundred blazes have scorched more than 30 hectares (74 acres) of forests, according to data from the European Forest Fire Information System. (AFP)
