Severe rain and flooding has continued to disrupt travel for commuters and led to the cancellation of rail services.
The Met Office issued an amber "be prepared" warning for Thursday evening as heavy rain again fell across London and south-east England.
Referendum polling stations in Kingston and Barking were forced to close as 40mm (1.5in) of rain fell earlier.
And London Fire Brigade said it had attended more than 400 incidents, including properties hit by lightning.
Commuters faced severe disruption with some stations closed because of overcrowding and floods forcing the closure of roads.
- Southern advised commuters to "start your journey home early" because of heavy rain forecast for the evening rush hour
- All lines affected by flooding on London Underground have reopened, although there are still delays reported and Balham station remains closed
- Rail companies including Southeastern, South West Trains and Greater Anglia are reporting major problems and Gatwick Express has a reduced service
- Waterloo Station was closed because of overcrowding while other stations were very busy as commuters tried to board services home
- Flooding have closed roads in Clapham and Raynes Park while there were delays in Brixton after a collision between a bus and a fire engine
In Chessington, resident John Tindall said there was about 15cm (6in) of fast flowing water in the polling station on Devon Way when he tried to vote earlier on Thursday.
Kingston Council said it decided to close a polling station and move it to the Hook Centre.
The Shiraz Mirza polling station has also been moved to Malden Manor Children's Centre in Lawrence Avenue, while the polling station at St Thomas More Catholic Church in Barking was shut because of a burst water main.
In Kent, a Dover polling station was being run on a generator because of a power outage, Dover District Council said.
UK Power Networks said electrical equipment became submerged in the floods, causing power cuts across the region, but it said everything was being done "to restore power as soon as possible".
The Environment Agency has issued six red flood warnings while rivers in Bromley and Sidcup in south-east London, and Basildon, Essex, have been affected.
Forty flood alerts are currently in place:
Some people in Barking had to be rescued from their homes by London Fire Brigade crews using boats.
While in Romford, a couple who are set to become first-time parents were forced out of their ground-floor flat after water began "pouring" into the building overnight.
David Sandor and his wife Lidia, who is eight months pregnant, said they would not be able to return to their home for two months because of the damage.
A teenager and his dad were also rescued by fire crews near Romford after they were caught in flood water in Colliers Row while trying to get to school in Croydon.
Paul Greaves described the area as "gridlock… because of the rising water" and said he and his son Josh were "lucky".
Rescuers had been in the area when they left their car and tried to walk to a nearby station.
Fire crews spent two hours pumping 1m (3ft) of water out of a basement at Wimbledon College of Art after smoke filled the boiler room.
Students said they were meant to receive their marks on Thursday but have been told they will have to wait, while a number of their sculptures, created for the college's summer show, had been destroyed.
Carol Baker, from Basildon, said her daughter Nicola nearly missed taking her Biology A-level exam in East Ham because of disruption on the roads.
She said the pair left their home at 06:30 BST but did not arrive at the school until 11:00 because of the weather, although teachers still allowed her to take the paper.
"She had been crying on the commute as she was worried they wouldn't let her take it," she said.
Several overground rail services have also been impacted by the weather.
Commuters were evacuated from trains at West Norwood station after smoke started billowing from the flooded track.
Travellers at Clapham Junction said they were faced with a "mass of bodies" as they tried to board services into central London.
A Network Rail spokesman said: "Staff have been out all night and are still out in the rain working with pumps and repairing damage.
"We are doing all that we can to keep trains running," he said.
BBC Weather said there were more than 1,000 lightning strikes across the UK overnight and a month's worth of rain had fallen in London since 18:00 BST on Wednesday.
The Met Office said the rain was brought on by increasingly warm and humid air arriving from France.
Forecasters are warning of the potential for a "second wave" of downpours late on Thursday.
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