Thunderstorm warnings are in place for most of England after heavy rain and flash flooding brought disruption to roads and railways on Thursday night.
The Met Office has issued yellow thunderstorm warnings until Monday, with the potential for flooding and damage to buildings from lightning and hail.
Downpour is forecast to arrive at around 3pm this afternoon in south London, progressing to storms throughout the evening and night.
Heavy rain which lashed southern England on Thursday afternoon forced parts of the M25 to be closed, while passengers were evacuated from a train which became stuck following a landslide in Kent.
The Roads Policing Unit for Surrey Police tweeted the M25 was closed between junction six and eight to allow authorities to pump water off the road and allow those trapped on the hard shoulder to make their way through.
More than 20 cars were stranded in feet-high water in one stretch, according to onlookers.
Meanwhile, 19 people were evacuated from a train which became stuck following a landslide, according to British Transport Police.
The train came to a halt between West Malling and Borough Green in Kent and rescue attempts were hindered by localised flooding, Network Rail said.
A tweet by Network Rail Kent and Sussex said teams would be working overnight to clear mud which was washed onto the railway by torrential rain in the area.
Met Office chief meteorologist Frank Saunders said: "Up until Monday, thunderstorm warnings cover much of England and Wales, with parts of southern England and South Wales seeing the greatest likelihood of impacts.
"The storms will not affect all areas, but where they happen there will be frequent lightning, gusty winds and intense, heavy downpours with 30 to 40 millimetres of rain possible in less than an hour and, in a few unlucky spots, a small chance of 60 mm falling in a short period.
"With the continuing hot weather, large swathes of the UK continue to be at risk from thunderstorms, and potentially the impacts from heavy rain, into the early part of next week."
Neil Davies, Flood Duty Manager at the Environment Agency, said: "Isolated thunderstorms could bring sudden surface water and river flooding, which may lead to flooded properties and severe travel disruption in some areas. Further surface water and river flooding is also a possibility until Sunday."
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