The persistent heavy downpours that have swamped much of the country will continue today and cause some areas to experience a whole month's rainfall in just 24 hours, weather experts say.
Communities across England and Wales are bracing themselves for the risk of floods from rivers and surface water as up to 100mm, almost four inches, of rain could fall by the end of the day, the Met Office said.
In England the Environment Agency has issued 55 flood warnings for the South West, the Midlands, Wales, the North East and North West, and 164 less serious flood alerts in the South East and East Anglia.
The Pennines are likely to receive the heaviest rain, leading to an increased risk of flooding for communities around the rivers Aire and Calder.
Strong winds are also expected to batter parts of Northern Ireland and Scotland, with gusts of up to 70mph along coastal areas later this morning.
A significant number of flood warnings could be issued over the coming days as the wet weather looks set to persist over the UK until the middle of the week.
Tom Tobler, a forecaster with MeteoGroup, the weather division of the Press Association, said Wales and northern England would see much of the heaviest rain today.
He said: "Further south and east, and in central and southern England, there will be some sunny spells.
"But there will be heavy showers coming in along the south coast and Kent. Places like East Anglia will be fairly dry, with just the odd shower.
"The heavy rain will be across the north west and north east, which have already had a lot of rain since yesterday, and there will be a risk of flooding."
Mr Tobler said parts of England and Wales had experienced up to 50mm of rain up to 6pm yesterday, and a further 25mm to midnight, with 5mm falling every hour in many areas.
He said: "It is the persistent nature of the rain, rather than it being torrential, so it just adds up."
The rain has already caused floods and travel chaos.
The Environment Agency is urging people to be prepared for flooding, keep an eye on local weather reports and sign up to its flood warning service. People are also being urged to stay away from swollen rivers and not to attempt to drive through floodwater.
Heavy rain yesterday led to more than 100 properties flooding, with some 42 properties in the South West, 35 in the Midlands and 20 in the South East hit by surface water floods.
There was widespread disruption and long delays to rail services in the South West, the Midlands, northern England and Wales, with the lines between Exeter and Bristol, and Wakefield and Leeds among those hit.
The AA said it had been called out to more than 200 vehicles driven through or stuck in floodwater.
Devon and Somerset Fire Service responded to dozens of reports of flooding, with water up to 3ft deep in some properties in Wedmore, near wells, Somerset.
Avon Fire and Rescue Service said people had to be rescued from cars in water and flooding in homes in Bristol, North Somerset and South Gloucestershire.
The heavy rain and flooding is the latest to hit parts of the UK this year, which saw drought in the spring give way to repeated downpours leading to the wettest April on record and thewettest summer for 100 years.
Six people had to be rescued from vehicles stranded in floodwater in North Yorkshire overnight, the fire service said.
North Yorkshire Fire and Rescue Service said it received more than 80 calls to incidents related to the heavy rain.
Five people were rescued from their vehicles in the Skeeby area and one was rescued in Whashton.
Several cars had to be removed from standing floodwater on the A1, where the River Swale intersects the road at Brompton on Swale.
A fire service spokeswoman said the majority of calls were received between 4pm and 10pm yesterday.
And a large number of calls related to flooded properties in the Harrogate area, including a school at Summerbridge, where fire crews helped to place sandbags to try to divert the water away from the building.
The spokeswoman urged motorists to take extra care while out on the roads, although the situation was said to be improving.
She said: "There are high levels of standing water on the roads, therefore motorists should avoid driving through any floodwater and only make journeys if absolutely necessary until the weather conditions improve."
Rain caused flooding on roads across Tyneside and County Durham ahead of the main morning rush to work.
Durham and Northumbria Police issued warnings about the driving conditions.
A Durham Police spokeswoman said: "Due to persistent rain throughout the night, many roads in Durham and Darlington have been affected by flooding and some are currently impassable."
Flooding affected the A19 around Wingate, the A66 Sadberge to Cleveland, as well as smaller roads around Derwentside, Bishop Auckland and Sedgefield.
Northumbria Police Chief Inspector Sarah Pitt said: "Acting on the information from our partners, we are getting extra officers out to the areas that are most affected to offer reassurance and support for local people.
"We continue to advise residents that might experience flooding to get advice from the relevant agencies and to be as prepared as possible.
"Anyone caught out by the rain and on the roads should stay calm and avoid any flooded roads and areas where possible."
Flooding affected major routes including the A1 northbound between the Coal House roundabout and Lobley Hill at Gateshead, the A19 around the Testos roundabout in South Tyneside and smaller routes in North Tyneside.
In Morpeth, Northumberland, some people were evacuated from their homes as floodwater rose.
A Northumbria Police spokeswoman said: "Residents in an area of Morpeth are being evacuated as a precaution.
"We are working with the local authority to take them to an alternative location."
The Environment Agency said parts of Yorkshire and the North East had experienced a month's rain in just 24 hours.
Network Rail reported there were no train services between Newcastle and Edinburgh because of the heavy rain, and passengers would be diverted via Carlisle.
Drivers on the A1 at Dunston, Gateshead, had to be rescued from their cars by police, an ITV journalist said.
Rachel Sweeney, who works for Tyne Tees television, said on Twitter: "My car is stuck! I'm in a van with a prisoner and two cops called Emma and Alec!"
She said she had to jump in her high heels into the police vehicle.
The Wear burst its banks at Cone Terrace, Chester-le-Street, County Durham, police said. Officers were in attendance.
Ten people were taken to safety on inflatable rafts by firefighters after flooding near their homes in St Helens.
Merseyside Fire and Rescue Service was called to Blackbrook Road, St Helens, at 4.23pm yesterday after water flowed over a nearby brook's banks following heavy rain.
Around 1ft (30.5cm) of water had risen near houses in the road.
Fire crews used an inflatable boat to take residents, along with a cat and a dog, to safety.
The flooding affected the junction of Blackbrook Road and Westend Road, not far from the Ship Inn.
Station manager Steve Pratt said: "There were people who needed our help after floodwater entered the ground floor of a number of properties in Blackbrook Road.
"Our firefighters and the Search and Rescue Team train to deal with this type of situation and put safe systems in place to ensure people were brought to safety."
There were no reports of any injuries.
Merseyside Fire and Rescue Service also said that more than 20 homes were evacuated in Fouracres, Maghull, last night.
Some residents left their homes to stay with friends and family, while many people just moved upstairs, the fire service said.
There are currently 17 flood warnings and 37 flood alerts in place across the North West, the Environment Agency said.
North Wales Fire and Rescue Service said it had been "busy" attending flooding incidents across the region throughout the night but the situation has now subsided.
The incidents attended mainly involved surface water and overflowing drains, with some water entering homes, but with no homes or buildings seriously affected.
Flintshire remains the most affected area, although incidents have also been reported in Wrexham, Conwy, Denbighshire and Anglesey.
Since 4pm yesterday, 18 flooding-related calls were received by fire and rescue service control room operators and crews have attended 14 incidents.
At 9.48pm yesterday, a 43-year-old man was rescued from his vehicle which was submerged in deep water in Chester Road, Sandycroft.
He was taken to hospital by ambulance for a precautionary check- up.
Earlier, at 7.28pm, crews were called to a caravan park in Llangollen where three caravans were affected by floodwater which was pumped away.
In Anglesey, at around 1am this morning, a crew was called to Wellington Street in Llanerchymedd where a river had flooded and water had to be diverted.
Paul Jenkinson, from North Wales Fire and Rescue Service, said: "We advise the public to heed warnings in the media in relation to travelling advice from North Wales Police - when there is so much surface water is is best not to travel unless absolutely necessary.
"And if you are faced with floodwater, do not try to drive through it as it may be much deeper than it looks."
One of the main roads into Newcastle has been shut so a wall can be taken down, police said.
The A1058 Coast Road in Wallsend was closed to allow workmen to relieve water pressure by demolishing the wall.
Police in Cumbria dealt with more than 30 separate incidents of highway flooding overnight, with many of the roads in the county affected by surface water.
Lanes were closed on the M6 northbound just north of junction 41 due to standing water, a police spokesman said. One lane was open to allow traffic to pass with care.
Train services in Lancashire were also affected by the rain. Northern Rail said the Wigan Wallgate to Southport and the Blackburn to Clitheroe lines were closed due to flooding and replacement buses were operating.