Flood warnings remain in place in many parts of the UK as heavy rain continues to cause disruption.
There are 66 flood warnings and 164 flood alerts in England and Wales, and nine flood alerts in Scotland.
The Met Office issued a red severe weather warning - meaning take action - for rain in south-west Devon and east Cornwall, which came in at midnight.
Environment Agency officials have been visiting campsites in these areas to warn holidaymakers.
A red warning from the Met Office is the highest level on its warning system, and means people should take action to protect themselves and their properties rather than just being aware (yellow) or prepared (amber).
BBC weather forecaster Peter Gibbs said a large area of rain had been concentrating over south-west England.
"That's why we've got a red severe weather warning from the Met Office. That's the highest level that we issue, and the reason is that the rain just isn't going to move on," he said.
He said there could be as much as 60-70mm (2.4in-2.8in) of rain in some spots on Saturday, and 20-40mm more widely in the area.
Meanwhile, 20,000 ticket holders have been asked to stay away from the public car parks at Saturday's Formula One Grand Prix qualifying sessions at Silverstone, on the Northamptonshire/Buckinghamshire border.
Heavy rain affected thousands of race fans on Friday and left half of the circuit's car parks unusable. Officials want to ensure they are in use for Sunday's race.
And a A police command centre has been set up in Sheffield over fears of flooding, while an extra 150 South Yorkshire Police officers were called in to work on Friday night.
The Met Office said a low pressure system was set to bring rain and thundery showers to the UK until early next week.
Met Office chief forecaster Frank Saunders said: "Although not all places will see the heaviest of the rain, where it does fall it is likely to lead to surface water flooding and disruption to travel.
"The South West of England looks the most likely area to see heaviest rainfall through Friday night and into Saturday with the greatest impacts."
Outside of the Met Office's red warning area, which covers Plymouth and Exeter, much of the rest of the South West is covered by an amber warning.
Amber warnings are also in place for the areas covered by Central, Tayside, Fife, South West Scotland and Lothian Borders, with most of the rest of the UK covered by yellow warnings.
Craig Woolhouse, the Environment Agency's head of flood incident management, urged people to remain on flooding alert, particularly in Devon, Cornwall and Somerset.
"When flood warnings are issued, residents in those areas should think about moving valuable possessions to safety," he said.
"We would also ask people to remember to stay away from flood water, and do not walk or drive through it, as it is often fast moving and can contain sewage and other debris."
The agency has opened incident rooms and has teams out checking on flood defences and clearing any blockages to reduce risks as much as possible.
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