Roads in parts of southwest England have been flooded in a second day of heavy rain and thunderstorms.
England and Wales are covered by a yellow thunderstorm warning, with more flash flooding, transport disruption and power cuts likely, the Met Office said.
Southern England will remain under the warning on Wednesday, forecasters said, adding that communities could be cut off by flooded roads and the floods could be dangerous.
The Environment Agency had 28 flood alerts - indicating flooding is possible - in England as at 8pm. No flood alerts are in place for Wales and Scotland.
One of the reasons for the concern is that the heavy rain follows weeks of drought conditions - when the ground is too dry, it can't absorb the rain fast enough, so the water runs over the land and floods it.
The Met Office said that Monday marked the eighth consecutive day with the temperature hitting 30C (86F).
Parts of southwest England, southern and central England, and the east of England were already officially in drought, and Yorkshire joined them on Tuesday.
The A358 near Combe Florey in Somerset was closed on Monday and for most of Tuesday due to a mudslide, with authorities saying more than 50 tonnes of mud were removed from the road.
Social media footage showed torrential rain and flooding on roads in Cornwall and Devon, and other affected places included Haywards Heath in West Sussex, Port Talbot in south-west Wales, and Bridport in Dorset.
Downpours also hit parts of London, with pictures showing people donning ponchos and shielding under umbrellas.
Surfers Against Sewage also warned that storm sewage discharge was affecting beaches in Cornwall, Devon, Sussex, Essex, Lancashire, Lincolnshire, Northumberland, and Cumbria.
The group warned people to check their interactive map online before swimming.
ScotRail said that its station in the Scottish city of Perth had been flooded and that passengers everywhere should expect delays, with speed restrictions on some routes.
Met Office spokesman Stephen Dixon said parts of the country could see up to 50mm of rain within three hours, with slow-moving thunderstorms in the Midlands moving south as the day goes on.
Mr Dixon said this risk will continue overnight and throughout Wednesday.
"Early on Thursday morning, the main risk that we are looking at is for the South East," he said.
"The risk then decreases as the day goes on."