Flash flooding has seen people rescued from submerged cars and hundreds of calls made to emergency services as torrential rain and thunderstorms batter parts of the UK.
The Met Office has issued yellow rain warnings for Tuesday afternoon and evening in central, western and southern parts of the UK, extended to 6am on Wednesday for the South East.
A spokesman for the Environment Agency told the Press Association that 35mm of rain had been logged in an hour in south London.
London Fire Brigade said it had received more than 100 flood-related calls, and had attended incidents thought to have been caused by lightning, including trees, hoardings and telegraph poles being set alight.
Two people were helped from their cars and another had to be rescued by fire crews after three vehicles became submerged in two metres of water on Manor Road in Wallington at around 2.21pm.
The London Ambulance Service tweeted that a man they checked over at the scene didn't have to be taken to hospital.
A fire service spokesman said: "Our 999 control officers have been extremely busy this afternoon taking calls to storm-related incidents across the capital.
"Firefighters are attending a number of incidents, mainly due to flooding. Crews rescued someone from a car that was almost completely submerged by floodwater in Wallington."
Grahame Madge, forecaster for the Met Office, said the downpours could continue to cause localised flooding, surface water flooding and travel disruption.
He added: "What we have is a situation where we have warm, very moist air coming in from the continent and the heat added to the warm air causes it to rise and sees the development of these showers.
"The intensity of those can be very severe in localised areas - as we have seen in some places like London and Brighton there has been very heavy rainfall. And that has led to flooding in some areas - which is exactly why we issued the warnings."
Images and videos of flood-impacted areas, featuring submerged roads and water-logged streets, have since been shared on social media.
Madge added: "It is the intensity of rainfall that comes from these types of showers that can lead to waters rising very quickly because it can happen over a short space of time."
Between 1am and 4pm on Tuesday the Met Office recorded 47mm of rainfall at Kenley Airfield in Surrey, 29.6mm in Ravensworth in North Yorkshire and 21.2mm in Lough Fea in Northern Ireland.
Referring to the 35mm logged as falling in an hour in south London by the Environment Agency, Madge said it was an "exceptional" amount.
"We would have expected in an average June 49mm of rain to have fallen in London on average across the month - it is significant," he added.
With temperatures reaching 24C in Manchester, 22C in Cardiff, 21C in Glasgow and 20C in London on Tuesday, another warm day is expected on Wednesday.
The Met Office predict the mercury could reach 23C in Birmingham and 25C in London, but says that these temperatures will cool down as the week progresses.
"Most places look like they are going to be affected by rain from Friday morning and Sunday evening," said Madge as he described the weekend weather front that will be moving in.