Forecasters say that the mercury has already hit 31C in Manston, Kent, with chances it could continue to climb this afternoon.
It comes as the UK enjoys an Indian summer after temperatures hit 29.8C in Porthmadog on Monday.
As it starts to cool after tomorrow, most of the UK will still continue to see bright, dry conditions until Sunday.
We've some very #warm temperatures across the southeast today ☀️ 🌡️
However, the #weather is set to cool down over the coming days with daytime maximum temperatures returning towards what is normal for the time of year, especially so in the north 👇 pic.twitter.com/8a2pYYtNFu
— Met Office (@metoffice)
Met Office meteorologist Martin Bowles said that the country has been seeing "reasonably unusual" temperatures for this time of year, although the September record of 35C has not been broken.
He said: "The current weather just about covers our heatwave threshold of 27C for south east England for at least three consecutive days.
"The highest temperature recorded today has been 31C in Manston in Kent but that could get warmer," he added.
Mr Bowles said that Wednesday will see highs of 29C in the south east but temperatures will begin to drop in the north and midlands.
He said: "It will be a dry and warm day for most of the UK but temperatures start to drop significantly after tomorrow."
Mr Bowles said that Thursday, Friday and Saturday will likely see highs of around 21-23C.
However, conditions might start to change on Sunday with showers and clouds sweeping in.
"After seeing European weather, with the warmth coming up from France and Spain, we could see a return to more Atlantic conditions on Sunday," he said.