Flash flooding has caused travel chaos in parts of England as thunderstorms dumped almost half a month's rain in some parts overnight.
A train from Milton Keynes to Euston derailed near Watford Junction, injuring two people.
The worst-hit areas are across the east, south and south-east of England which all have amber warnings in place, according to the Met Office.
Roads, homes and a hospital are flooded with lightning damaging buildings.
Live updates on flooding and disruption
Train derailed by landslide
In pictures: Flash flooding
For key updates see BBC Weather and BBC Travel.
The disruption includes:
- The derailment of the London Midland 06:19 BST service from Milton Keynes to Euston near Watford Junction
- All London Midland services cancelled out of Euston until further notice
- Reports of lightning striking houses in multiple locations including Bracknell, Caversham, and Bournemouth
- The flooding of a maternity unit at Wallingford Hospital in Oxfordshire, with women going into labour to be sent elsewhere
- Waterlogged roads and rail stations, including Didcot Parkway, Newbury and Chieveley stations across Oxfordshire
- Major delays on the M25, M4 and M40 due to flooding
- Reports people are trapped in their houses in one flooded street in Oxfordshire
- Thousands of homes without power
'Major disruption'
Network Rail said CrossCountry, Great Western Railway and South West Trains were all affected with severe delays on dozens of services.
London Midland said the derailment had a knock-on effect on it trains, with hours of delays expected to last throughout the day.
The Met Office issued an amber weather warning, the second highest alert, for the East of England, London and the South East.
There is the the potential for "exceptionally large amounts of rain within a few hours" with frequent lightning and hail as additional hazards, forecasters said.
Whilst there remains some uncertainty about developments and areas affected, there could be major disruption, it added.
Image copyright Dorset Fire and Rescue Service'My mum panicked'
Mashood Shah, who lives at Walton Terrace in Woking, is one of hundreds of people across the country whose homes have flooded.
He described the moment water came pouring under his front door around midnight.
"My mum just said 'the water's all coming in' she was panicking. I had my wellington boots by the bed.
"I put them on and I came rushing down. I told my little brother 'stay up there, I will pass you everything'.
"The water came nearly to the top of my wellington boots."
He said sand bags were dropped off by the council about seven hours later.
Thames Valley Fire Control said it had received "an enormous number of calls" since 18.00 BST on Thursday for Berkshire alone.
"There were a total of 174 calls which resulting in 158 incidents, 47 of which were flood related," a spokesman said.
Met Office meteorologist Martin Combe said 32.8mm of rain had fallen in just three hours in Farnborough, Hampshire - nearly half the 70mm average for September.
He said: "The showers and thunderstorms are going to carry on for quite some time moving slowly north and eastwards, remaining around London through the morning and all afternoon in East Anglia.
"They will eventually clear off to the east, but it will be cool behind them. While it won't be any colder than average it is going to feel a lot cooler than it has been."
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