Hundreds of houses and businesses have already been swamped with floodwaters, while many more are at risk of rising waters.
Although the rain will be less persistent and punctuated with sunshine throughout the day, it will add pressure to already saturated ground and swollen rivers.
The worst affected areas will be northern Scotland, south-west England and areas along the south coast from Cornwall to Kent, along with Wales.All have already seen flooding in the last few days.
Thunderstorms will also greet parts of Dorset and Hampshire on Christmas morning.
David Jordan, the EA's director of operations, said: "Although the rain is set to ease a little in the coming days, the ground is still very wet and river levels remain high, so we would ask people to keep up to date with the latest warnings and stay prepared for flooding."
In Scotland 12 flood warnings were issued along with seven flood alerts. The Environment Agency has also issued 166 flood warnings across England and Wales, urging people to take immediate action against expected flooding.
It also has put 266 flood alerts in place, warning residents to be prepared.
The EA said around 470 properties have flooded since Wednesday, while Floodline revealed it has received 18,000 calls during the recent wet weather.
In Devon and Cornwall 245 properties flooded over the weekend and although a number of people were evacuated, most have now returned home.
Officials said the rivers Severn, Trent, Avon and Thames are at most risk of flooding.
Matt Dobson, a meteorologist for MeteoGroup, the weather division of the Press Association, said: "There will be showers sweeping from west to east across the UK today, and while they will not be as persistent as recent days, they will still be heavy.
"The ground is saturated after a good dose of rain yesterday, so the areas that have been hit by flooding won't welcome more with more local flooding certainly possible.
"Up to 10mm will fall in the worst affected areas such as Devon and Cornwall as well as Wales and southern coastal areas of Hampshire, Dorset, Kent and Sussex.
"But there will be bursts of sunshine between the showers.
"There will also be thunderstorms and lightening sweeping up over Dorset and brisk winds across the south-west."
Yesterday the EA removed a severe flood warning - meaning there is "danger to life" - for the River Cober at Helston in west Cornwall, a town that has already seen residents evacuated from their homes.
The rain caused travel disruption on road and rail networks on the days leading up to Christmas, with a number of key routes struck by weather related delays.
The soggy Christmas comes towards the end of what is expected to be one of the wettest years in Britain since records began.
The UK's average rainfall in 2012, excluding December, is 1,202mm - placing it 13th in the list of wettest years since records began in 1910.
The year 2000 remains the UK's wettest year, with an average rainfall of 1,337.3mm.
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