Tuesday saw Britain swelter in temperatures which peaked at 33.5C (92.3F) in Brize Norton, making it hotter than Barcelona.
Despite being in the midst of a heatwave, the Met Office has issued a yellow weather warning for severe thunderstorms, large hail and strong winds which could lead to flash flooding.
The warning has been issued across all regions other than south-west England, London and south-east England.
It states that hot, moist air spreading north and north-east is expected to produce thunder storms, with some places seeing around 30mm of rainfall in an hour, and more than 50mm in a few hours.
The warning says: "Whilst most places will miss the worst, please be aware of the risk of localised flash flooding. Frequent lightning, large hail and strong winds could be additional hazards.
"All of this could lead to some flooding of homes, businesses and transport networks. Disruption to power is also possible."
The flooding could see further disruption caused to train services, some of which were delayed after heat-related speed restrictions were brought in.
Temperatures are expected to remain high across the country, with the south-east of the country seeing the best of the weather with thermometers hitting the the low 20s.
The London Ambulance Service said it had had 300 more calls than usual and the RSPCA said it had also seen a spike in calls from members of the public concerned about dogs left in hot cars, conservatories, sheds and caravans.
Dr Angie Bone, head of extreme events at Public Health England, said: "Older people, those with underlying health conditions and young children may all feel the ill-effects of heat over the coming days."
Scotland also basked in sunshine on Tuesday with temperatures in the high 20s as far north as the Highlands.
Alex Priestley, a Met Office forecaster based in Aberdeen, said: "The highest temperature that we have seen today was 28.3C in Prestwick, Ayrshire. Threave in Dumfries and Galloway was 27.8C and Kinlochewe in Wester Ross was 27C. In the cities, Glasgow was 26.8C, Aberdeen was 25C and Edinburgh was 24C."
However, he warned Scotland to brace itself for thunder, lightning strikes on power transmitters, hail, gusty winds, flash floods, river flooding, property flooding, surface water and slippery roads, with two bands of heavy rain sweeping in on Wednesday.
He added: "We have been liaising with responder communities and Sepa (Scottish Environment Protection Agency) and they're prepared for dealing with any issues that may arise."