A reading of 27.9C in Wisley, Surrey, surpassed the previous record of 27.8C from April 2001, the Met Office said.
The hot weather is way above the average maximum temperature for April, which sits at 11.4C.
At 27.9C it is the hottest day of the year so far beating the high of 25.3C that was recorded in St James' Park in London on Wednesday.
Temperatures in the UK are hotter than in Ibiza, Athens and Kingston, Jamaica.
The current summery spell comes as a result of warm air from the Azores, off the coast of Portugal.
The warm air has been dragged up towards the UK by the combined efforts of an area of low pressure over the Atlantic and high pressure over Western Europe.
Across the country people are enjoying the weather, with ice cream vans returning to the streets.
The warm weather is expected to last until the weekend and on Saturday evening Northern Ireland and Wales could see thunderstorms. This will bring with it cooler conditions and temperatures will be back down to 16 degrees in London by Monday.
Competitors in the London Marathon on Sunday can expect hot and humid conditions with a forecast of between 21C and 23C.
Temperatures could climb higher than the 22.7C recorded in 1997, the year of the hottest previous marathon.
Meteorologist Alex Burkill said: "There could be a shower but it's not very likely. It's not great conditions for running. In fact if any showers do come they might be very welcome."
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