Three days of temperatures of around 30ºC in the south of England have ended in thunderstorms, torrential rain, flash flooding, and warnings of travel chaos.
The Met Office has issued an amber warning of rain and the Environment Agency has six flood warnings in place.
A train derailed at Watford Junction after it hit a landslide, causing severe disruption between London Euston and Milton Keynes. One man was treated for a neck injury and one woman was treated for chest pains.
Due to a derailment this morning, there will be delays and cancellations. Ticket acceptance in place on other train operating companies
Euston station was packed with commuters following the derailment and landslide.
Stations including Didcot Parkway in Oxfordshire and Brookwood in Surrey were severely waterlogged.
Many parts of England experienced thunderstorms overnight, including in Barnsley, South Yorkshire. A motorist recorded this video of flooding on the M25.
There is also severe disruption on roads in the South East, including on the M4 and M40.
Maidenhead town centre, the M4 and A34 near Newbury, Chieveley and M40 are particularly affected #TVPfloods https://t.co/kbD0Aq54jz
Jonathan Day, flood risk manager at the Environment Agency, said: "In the early hours of Friday morning showers will become widespread and torrential. This may lead to flooding, particularly across large parts of the south, including London, which could cause significant disruption during the morning rush hour."
He added: "We urge people not to drive though flood water – it is often deeper than it looks and just 30cm of flowing water is enough to float your car – and check travel arrangements."