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 had been "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.
Mr Austen said two sisters lived at the property, adding that one resident who was attended by paramedics "seemed shaken but OK".
"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.
While it was a wet and stormy start for many in the south of England, Northern Ireland and western Scotland saw sunshine and temperatures approaching 28C on Saturday.
The Met Office thunderstorm warning for southern England and Wales was in place until 22:00 BST on Saturday.
A second yellow warning for thunderstorms is in place from 05:00 BST to 00:00 BST and covers most of southern England, areas of central England and south east Wales.
The Met Office has warned the heavy showers and thunderstorms could result in flooding and disruption to transport in some places.
It comes as many people set off for their summer break this weekend with the school holidays beginning across parts of the UK.
Torrential rain and electric storms are likely to affect those attending the Latitude Festival in Suffolk, with the Met Office yellow warning stretching into East Anglia.
Cooler weather is predicted across the UK from Sunday, with further heavy showers and thunderstorms pushing in from France across southern and eastern England.
BBC Weather's Alina Jenkins said an area of low pressure meant that "for much of next week, the theme is showers, longer spells of rain and it will be feeling cooler, both by day and by night."
It comes as the UK recorded its hottest temperature of the year so far on Tuesday - 32.2C at Heathrow Airport in west London.
In the same week, the Met Office issued its first extreme heat warning for areas of the UK. The alert covered large parts of Wales, all of south-west England and parts of southern and central England.
Have you been affected by the bad weather? Get in touch by emailing firstname.lastname@example.org.
Please include a contact number if you are willing to speak to a BBC journalist. You can also get in touch in the following ways: