Travellers face disruption during Friday's morning rush hour after torrential rain and thunderstorms lashed parts of the country - with forecasters warning that more severe weather is on the way.
An amber weather warning - meaning a potential risk to life - remains in place for the south-west of England and south Wales until 6am, and forecasters have warned of difficult driving conditions and flooding.
A yellow warning covers the south of England until 9am, while another is in force for Scotland, Northern Ireland and the west of England between 9am and 10pm.
Met Office meteorologist John West said a "lively" day was in store on Friday, despite a bright start for some.
He said: "It will be a warm and humid day, with some decent spells of sunshine. But with the temperatures rising and an awful lot of moisture in the air, we'll see more heavy showers and thunderstorms returning by early afternoon.
"This will affect Northern Ireland, Scotland and western parts of England and Wales.
"With some torrential downpours, it is likely that we will see some localised flooding."
Forecasters predict up to 1.8 inches of rain could fall in the space of an hour in some parts, rising to 3.6 inches over three hours.
It comes after storms and heavy downpours caused problems in some parts on Thursday afternoon and overnight, with disruption expected to continue into the morning.
Train passengers in the Midlands could find their journeys affected after lightning strikes damaged equipment between Birmingham New Street and Wolverhampton.
Network Rail said disruption was expected until about 9am.
South-west parts of England were worst-affected overnight, with Gloucestershire County Council reporting multiple calls to the fire service over flash flooding.
On Thursday evening, Didcot Parkway railway station in Oxfordshire flooded, leaving passengers to wade through deep waters or be helped by firefighters.
Travellers posted to social media to report raw sewage flowing from drains, while one commuter said she had been given a piggy back through a flooded underpass.
Flights were also cancelled due to the severe weather conditions, with 48 easyJet services affected at Gatwick Airport.
Ryanair cancelled a "small number" of flights, while others were delayed.
The Environment Agency has urged people to check their flood risk and warned people not to drive through flood water.
Kate Marks, Environment Agency flood duty manager, said teams would work "24/7" to operate flood defences, clear blockages in rivers and streams and support partners at any incidents of surface water flooding.
"With heavy rain forecast during rush hour, drivers should stay up to date with the latest weather forecast and travel information before making their journey," she said.
"We remind people not to drive through flood water as just 30cm can move your car."