Parts of London received a month's worth of rain in one day, causing flash floods.
On Monday 47.8mm of rain fell in a 24-hour period in Kew, most of it in just one hour. The average monthly rainfall in July is 44.5mm.
Residents were evacuated from their homes and train services cancelled, while cars were submerged in water.
London Fire Brigade said it had taken more than 1,000 calls related to flooding.
A spokesperson for the service said: "We're asking people not to walk through or drive through the floodwater. Floodwater can be contaminated and vehicles can become unstable."
Thames Water said it received more than 2,500 calls in five hours on Monday as sewers filled up and flooded.
"While our pipes are designed to cope with most storms, yesterday's rainfall was so severe the system filled up very quickly," a spokesperson said.
Among those to suffer was Queen guitarist Brian May, who lives in Kensington.
The rock star said he was "angry" after a number of his "precious" belongings were ruined during the flooding.
'Disgusting and heart-breaking'
In a post on Instagram, he wrote: "The whole bottom floor had been inundated with a sewage overflow - which has covered our carpets, rugs and all kinds of precious (to us) things in a stinking sludge.
"It's disgusting, and actually quite heart-breaking," the We Will Rock You writer added. "It feels like we have been invaded, desecrated."
Daisy King, from Holland Park, described how she came home to find more than two feet of water in her flat.
She said: "It was up to my knees and all my stuff was floating about in it.
"The fridge and oven were half-filled with water and books and records were ruined."
The owner of vintage record shop, Audio Gold, in Muswell Hill said "tens of thousands of pounds-worth" of his stock has been ruined in the floods.
"The two main things that were damaged were our records and the vintage wooden loud-speakers", said Ben Shallcross.
The businessman, who has owned the shop for 20 years, explained: "Much of the shop's stock is stacked on the floor and the water has swelled up around the beautiful old speakers and ruined the veneer."
One resident in Maida Vale said his basement was "under at least a foot of water, and it was black, so it is sewage water".
Shane, who lives on Shirland Road, said "everything was wrecked" by the floods which "subsided quickly" when the rain stopped.
Kensington and Chelsea Council said 120 people were put up in hotels on Monday night due to flooding in the area.
One video posted on Twitter shows water pouring in down the stairs at Sloane Square Tube station.
Putney Village in Wandsworth and Chipstead in Surrey both recorded more than 31mm of rain in one hour.
The rainfall recorded in Kew Gardens on Monday made it the wettest day there since 6 July 1983 and the third wettest day on record.
Gareth Furby, who lives in Barnes, south-west London, described "bailing out" water from a neighbour's front garden.
"I helped another neighbour by building a dam at her front gate," he said.
"A theory locally is that the rain came precisely at high tide on the Thames which meant any sewers which flow into the river backed up."
Underground stations, including Chalk Farm, Hampstead and Wimbledon, were closed due to the flooding.
Lines at Euston station had to be shut down after the intense downpours.
The train routes which were affected by floods included:
- Thameslink services
- The London Underground Circle Line, District Line and Hammersmith and City Line
- London Overground services between Richmond / Clapham Junction and Stratford
- Services into and out of London Euston
A lightning strike also damaged signalling at Epsom, affecting trains between London Waterloo and Dorking.
Operators have said trains could be cancelled or delayed with commuters advised to check before they travel.
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