The thermometer rose to 38.1 degrees Celsius (100.6 Fahrenheit) in Gravesend in southern England, shattering two new records of 37.4 and then 37.9 degrees set earlier in the day at Heathrow airport, meteorologists said.
The previous record since temperatures were first kept during the 1870s was 37.1 degrees Celsius (98.8 Fahrenheit), set in central England 13 years ago.
Millions of Britons have headed to beaches, lakes and parks in recent days as the country has been blanketed under the heat wave currently affecting much of Europe.
But the heat also sparked some violent storms, causing one death and over a dozen injuries.
One man was killed and another injured after their boat capsized while fishing near the northeastern town of Hartlepool.
In Birmingham, central England, 15 people were injured by a lightning strike at a football match.
One woman suffered a heart attack as the lightning bolt struck the pitch where an amateur game was taking place during a heavy storm, ambulance staff said.
At an agricultural fair at Stonehouse Farm in central England one woman was severely burned and five others received lesser injuries when lighting struck an umbrella.
The 100-degree heat will chill the hearts of the nation's bookmakers, who now face potential payouts in the million of pounds after heavy betting that the mark would be reached.
Workers at London Zoo also had a busy day keeping species used to more temperate climes from getting too hot and bothered.
"We are regularly hosing down the sloth bears and the pygmy hippos, who seem to really enjoy it," spokeswoman Debbie Curtis told AFP.
"The primates are getting frozen fruit and nuts, like a giant ice lolly. The penguins are getting the same, but made from fish."
Pub and bar owners were also enjoying a special treat -- an extra three million pints of beer are expected to be drunk this weekend as Britons quench their thirst, according to estimates.
The hot weather has been experienced throughout much of the country, with Scotland edging close to its own record temperature, a slightly more modest 32.8 Celsius (91 Fahrenheit) seen in 1908.
British temperature statistics go back to the mid-1870s, when a standardised global system for shielding measuring equipment from the sun was first introduced.
Met Office forecaster Roger White said he and fellow "weather nerds" were thrilled to see the 100-degree mark beaten.
"We tend to get fairly excited about these things because that's what interests us, that's why we joined," he said.
"It's an honour to be working on such a day."