London was spared the heavy showers and thunderstorms which plagued other parts of the country on Wednesday as it basked in sizzling 30C temperatures.
A heatwave continued in the south of the country, with a high of 30.2C recorded in the capital at Heathrow.
But the hottest temperatures were recorded in the village of Brize Norton in Oxfordshire, where the mercury topped 31.1C.
While expected thunderstorms did not hit the capital on Wednesday, where a yellow weather warning is in place until 11.59pm, a wider warning is in place for all of Thursday.
Some rain is forecast for London, where residents are being warned of a risk of “rounds of heavy showers”.
Met Office deputy chief forecaster Dan Holley said the most intense impacts of storms on Thursday were "likely to be focused on central, southern and South East areas of England".
He added: "Here some locations will witness torrential downpours, large hail and frequent lightning.
"A few places could see 50-100mm of rainfall in a few hours."
The Met Office said it was "likely" that some weather warnings may need to be issued at short notice ahead of the development of the most intense thunderstorm activity.
Tuesday was the warmest day of the year so far with a temperature of 32C recorded at Kew Gardens and Heathrow.
There was a large contrast in temperatures overnight on Tuesday with a minimum of 19.9C recorded on the Isle of Portland in Dorset and a low of 1.7C at Tulloch Bridge in Scotland.
Forecasters said it was a "pretty uncomfortable night for sleeping" in the South with "high temperatures, but also high humidity".
A Met Office spokesman said a weather front approaching from the northwest on Friday would bring "fresher air and the end of the heat" - with lower temperatures expected by the weekend.
The London Fire Brigade has urged people to be careful while swimming amid the warm weather.
Assistant commissioner for prevention and protection Craig Carter said the risk of drowning increased when schools break for summer.
Mr Carter added: "Often, young people are encouraged by their peers and aren't aware of the dangers - no matter how experienced a swimmer you are, it can be impossible to know how deep water is or how fast it is moving.
"Even on hot days, the water temperature can be cold enough to bring on cold water shock, causing panic, anxiety, disorientation and loss of muscular control. This can cause you to gasp for air and inhale water."
