A high of 25.7C was recorded at Heathrow Airport at 2pm on Tuesday, making it the hottest day of 2021 so far - topping the temperature of 25.1C set just one day before.
As millions enjoyed the first day of the meteorological summer, the Met Office predicted that the mercury would climb even higher later this week, with highs of 27C expected.
“The thunderstorms could bring lots of lightning, some hail, as well as some heavy rain, and with the half term there is an increased number of tourists in this area,” Met Office meteorologist Alex Burkill said.
“The thunderstorms do then push north-eastwards into the Midlands and across more of Wales, but they also ease and break up, so these places will see some showers but they won't be as intense.”
From 5am to 11am in the affected areas, the weather service has warned that there could be some short-term loss of power and other services, while delays to train services and poor road conditions are also possible.
Millions of Britons flocked to parks and beaches in recent days as the sun arrived in time for the spring bank holiday weekend, with members of the public enjoying the lifting of most lockdown restrictions.
Bournemouth beach was packed with sun-seekers on Sunday, while tourists to Edinburgh’s Portobello beach braved a misty morning before the damp air gave way to an afternoon of sunshine.
The run of warm temperatures comes after a month which saw heavy downpours and prolonged spells of rain across the country, with Wales recording the wettest May since records began in 1862, with 245mm of rainfall.
Meanwhile, the UK as a whole saw its fourth highest amount of rainfall on record for the month, with an average of 120mm.
Additional reporting by PA
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