Thunder and storms have started causing havoc in parts of the country after days of sweltering heat.
The Met Office has forecast changes for Wednesday
Government health warnings over the heatwave, which saw temperatures in London reach 31C, are still in place.
But the Met Office is warning of floods and high winds across southern and central parts of Britain on Wednesday.
Heavy rain and flash floods have already hit some areas, with power cuts across Northamptonshire. And a boy has been hit by lightning in south London.
The 16-year-old was taken to hospital with burns after being struck in Ashburton Park, Croydon, south London, the London Ambulance Service said.
The severe weather left many Northamptonshire roads gridlocked after traffic lights were knocked out.
In Shropshire, 60 homes had to be abandoned in the Cosford area after flooding.
Severe storms are expected to hit the south of England during the next 24 hours and work their way up through the country.
The Met Office earlier issued severe weather warnings for southern England, saying mini-tornadoes and flash flooding were possible.
It also warned that "large hail and squally winds" could cause hazards to some regions.
"The thundery weather, torrential nature of the rain and excessive heat are likely to ease from the west on Thursday," the forecasters said.
On Tuesday afternoon, part of London suffered showers while an inch of rain fell in just one hour on the coast of Cumbria and half an inch fell in a similar time period in Sussex.
Heavy rain, thunder and lightning also hit parts of southern Wales and south-west England.
Temperatures on Thursday and Friday are still likely to be in the mid 20s.
Wimbledon heat stroke
On Monday, continuing scorching temperatures prompted the Department of Health to raise its warning to level three.
That meant vulnerable people in care homes should be moved to cooler parts of the building and those living at home should be visited daily.
It is the first time the warning level has reached level three since the heatwave plan was introduced in 2004.
Monday was so hot that barristers and High Court judges were given permission to take off their wigs during court proceedings.
And Wimbledon tennis officials are considering allowing players more time to recover between sets after several fans and court staff were struck down by heat stroke.
A heatwave in north-west Europe three years ago caused 27,000 extra deaths.
In London, there was a 60% rise in the number of those aged over 75 who died.
The current hot weather is not causing such problems, but NHS Direct said it had been receiving about 2,500 calls a day more than on average.
People worried about their health during the heatwave are advised to talk to their GP, pharmacist, call NHS Direct on 0845 4647 or visit the website www.nhsdirect.nhs.uk.
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