Lightning has damaged homes in Hampshire and severe weather warnings are in place as the heatwave gives way to thunderstorms and torrential rain.
Two women escaped unharmed after a pair of houses in Andover were partially destroyed in the early hours.
The Met Office issued a yellow alert for storms, and warned of flooding, hail and 55mph gusts of wind in southern England and Wales.
It comes after days of extreme heat – and as many set off on summer holidays.
Hampshire and Isle of Wight Fire and Rescue Service tweeted a picture of two semi-detached properties struck by lightning in Andover’s Mercia Avenue. A spokesman said the roof was severely damaged.
Neighbour Barrie Austen said the roof was “completely ablaze”. “The side that supports the roof, that collapsed as well and then the flames spread into next door,” he told the PA news agency.
“I think the lightning hit the roof, woke them up and they just got out.”
The fire service said a 70-year-old woman had been assessed by paramedics but did not require hospital treatment.
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BBC Weather said that “after a very stormy start in the south” the thunderstorms had eased, but were expected to develop again later – reaching up to the Midlands.
Up to 50mm of rain is expected to fall within an hour in some southern counties of England later, with flooding possible.
Meanwhile the heatwave looks set to continue in Northern Ireland and western Scotland, with temperatures of 28C possible.
And despite the wet start in the south of England, it should remain dry and sunny in the north west of the country.
It comes as many people are expected to set off for their summer break this weekend, as the school holidays begin across large swathes of the UK.
Cooler weather is predicted across the UK from Sunday, with further heavy showers and thunderstorms expected across southern and eastern England.