Families had to be evacuated from their houses and dozens of drivers and passengers were rescued from cars after heavy rainfall overnight.
The worst-hit area was the south west where downpours left homes in up to 4ft of water and dual carriageways covered by 18in.
A 22-year-old woman from Poole, Dorset, died when her Vauxhall Astra went off the road and crashed on the A35 at Upton, Poole, during heavy rain.
A female passenger, also 22, escaped injury in the accident at 2.05am.
In the east of Cornwall, doctors were last night attempting to save the leg of an 83-year-old woman who had to be cut free from the wreckage of a vehicle after a high-speed road accident in "atrocious" weather. Three other people in the collision were also taken to hospital and all four were described as "lucky to be alive".
In Emsworth, Hampshire, 10 people were evacuated from their homes when a tree toppled on to a block of flats in heavy winds at 4.30am. The tree also crushed two cars parked in the driveway. No one was injured.
Train services were subject to "severe delays" on several routes between London and the South West.
The torrential rain began in the early hours and spread eastwards from Devon and Cornwall towards Gloucestershire, Hampshire, Dorset and Wiltshire, pushing as far north as Cheshire where firefighters rescued a woman from the roof of a car in Crewe after flooding.
The Environment Agency issued nearly 50 flood warnings, mostly in Devon, Somerset and Dorset, and more than 120 flood watches for rivers in the West and South West, northern England and Wales.
In Devon and Somerset the fire service received up to 300 calls during the night and fire crews rescued up to 20 people from vehicles and properties affected by flooding. Dozens of other people made their own way to safety.
A man and two women were pulled from a car by firefighters at Kilmington, near Axminster in Devon while a taxi driver was rescued in Plympton and two men were rescued in separate incidents at Monkton, Honiton.
Around 270 homes were flooded in Somerset, with water levels on some lower floors reaching up to 4ft. Fire officers provided sandbags and pumped out blocked drains.
The town of Ilminster was among the worst-hit. Other areas affected included Chard, Shepton Mallet, Street, Castle Cary, Wincanton and Yeovil.
Bridget Smith and her husband, from Ilminster, said she had to move into a hotel in Taunton after more than a foot of water came through the door. "It was like a river," she said. "It rained all night - I have never seen anything like it in 10 years living here.
"I was devastated when I saw all the damage. The electricity has blown, there's no gas, phone or anything."
Jane and Tony Bird, from Hempitts Road in Walton village, Somerset, told how their 11-year-old son, Jack, who was sleeping on a mattress downstairs with friends, woke up "floating" as most of the houses in their road were flooded.
A neighbour, Betty Mundy, 64, was mopping up her dining room and kitchen. "This is the first time it has happened here," she said. "I've had about an inch of water, and next door's had about a foot. I feel really upset. All my things are ruined."
Paul Eckardt, 56, a consultant engineer saw four inches of flood water pour into his 17th Century Grade II listed home in Crosscombe, Somerset.
"I didn't put sandbags out because there was no warning," he said.
"The next thing I knew I heard my neighbours moving about and I realised what was happening.
"All the village is pulling together and the local pub has provided coffees and a few stiff brandies to help with morale."
In Cornwall, nine people were rescued, including seven from two vehicles near Boscastle and three from a car near Launceston.
In Gloucestershire, flooding forced the cancellation of Cheltenham Races and the nearby village of Prestbury was also under water.
Many roads around the county were flooded, in Cheltenham and Tetbury but especially in the Forest of Dean. Motorists were advised to make only "absolutely essential" journeys.
In Cypress Gardens, Gloucester - one of the worst hit areas during the two floods last summer - the fire brigade pumped out drains as residents braced for more floods.
Fire and rescue crews were called out to homes in Crawley, Partridge Green and Turners Hill in West Sussex to pump flood water out of cellars as drains overflowed.
The Met Office said yesterday that drier weather was on the way. The rain will disappear in most parts of Britain from today. It will be cold, with overnight frost, but most areas are expected to be dry with some bright spells today and tomorrow.
There will be showers in some areas on Tuesday but Wednesday is likely to be dry and bright.
Firefighters were called to 80 flooded homes in Wiltshire, and dozens more in Fishguard, Dyfed and Stourbridge in the West Midlands.
