Temperatures are to reach as high as 27°C in Derbyshire this week - but predictions of a thunderstorm look set to dampen the heat.
The Met Office says there is a 90 per cent probability of heatwave conditions from today till Friday.
However, forecasts have also predicted isolated heavy showers or thunderstorms for Friday, July 27.
Today and tonight:
Highs of 27 °C. Cloud and rain over southern Scotland and Northern Ireland will slowly edge into northwestern parts of England and Wales. Dry with clear spells elsewhere.
Highs of 24 °C. A weakening band of showery rain will edge southeastwards into Wales and northern England. Fresher with showers in northwest. Mainly dry with hot sunshine elsewhere, especially in the southeast.
Outlook for Wednesday to Friday:
Mostly dry with plenty of sunshine Wednesday highs of 24 °C. Some rain in the north and west Thursday high of 27 °C, with increasing risk of thunderstorms on Friday 25 °C. Very warm or hot for most, especially southeast.
UK Outlook for Friday, July 27, to Sunday, August 5:
From Friday and through the following weekend a west/east split in the weather is expected, with cloudier, windier conditions in the west and northwest with some outbreaks of rain. In the east and southeast there'll still be some fine and sunny conditions, but with a risk of thundery showers moving north. Widely very warm or hot in the south and southeast, with warm and humid nights, whilst western areas may turn cooler. Through the rest of the period there'll be plenty of fine weather, but occasional rain in the west may spread to other parts at times, and there's an ongoing risk of thunderstorms, particularly across central and southeast England. Temperatures generally very warm away from the west, with hot or very hot conditions at times, especially in the southeast.