Heavy downpours and thunderstorms caused flooding in parts of London on Sunday.
There were many reports of vehicles becoming stranded as water quickly rose making roads impassable.
Rainwater flooded Tube stations and triggered stoppages of the electric trains.
The fire brigade said it had taken hundreds of calls – mostly about flooded basements or roads.
An amber thunderstorm warning is now in place for much of south-east England, with 100mm of rainfall forecast in some areas.
The Environment Agency has issued severe flood warnings for parts of London, and a number of less severe flood alerts have also been issued, covering most of the capital and parts of surrounding counties.
Resident Chris Date tweeted a photo of a bus in Walthamstow, saying, “It’s impossible to walk on the pavement. To get on that bus the water came up to my shins. This is a canal, not a road.”
Cyclist Eddie Elliott told the Press Association agency he had passed the area near Queenstown Road station to find the road totally shut down.
“Having been born and raised in London, I have never seen anything quite like it,” he said.
Elliott said the flooding was the worst he had experienced in the city, and described seeing “buses stood broken down in the water”.
A tweet from the Metropolitan Police Special Constabulary warned drivers they should not attempt to drive through floodwater if they find their route blocked.
The Met Office said the storms are being caused by a convergence of air currents as warmth in the earth’s surface from the recent heatwave rises into cooler air in the atmosphere.
Forecasters have warned travellers starting their summer holidays to expect floods, thunderstorms and strong winds.
Days of extreme heat last week have given way to cooler temperatures and unsettled, stormy weather in places.
Temperatures are set to rise again from Monday, with London expected to hit 26 degrees Celsius.
Parts of continental Europe are also experiencing unusual weather.
Reuters is reporting that the southern Belgian town of Dinant was hit by the heaviest floods in decades on Saturday after a two-hour thunderstorm turned streets into torrential rivers that washed away cars and pavements.
Dinant was spared the deadly floods that killed 37 people in southeast Belgium and many more in Germany 10 days ago, but the violence of Saturday’s storm surprised many.
“I have been living in Dinant for 57 years, and I’ve never seen anything like that,” Richard Fournaux, the former mayor of the town said.
There has not yet been an estimate of the damage, with town authorities predicting that it would be “significant”, according to Belgian RTL TV.