Many Brits are being hit by torrential rain, icy streets and flooding - with road closures hampering travel - as they try and return to work after festive celebrations with friends and family.
The Met Office issued a yellow rain warning for parts of south-west England and South Wales from 2am until 3pm today, Wednesday December 28.
People returning to work have been warned that travel will likely be hampered by heavy rain, which will move north-east throughout the day.
Homeowners and businesses have been told to prepare for potential flooding, which may cause disruption to power supplies and other services.
The Environment Agency has also issued 33 flood alerts.
Met Office meteorologist Rachel Ayers said: "We have a yellow rain warning in force from 2am tomorrow until 3pm. And that covers across Dartmoor and into the southern parts of Wales as well.
"We're looking at the potential of being 40-60 millimetres of rainfall in nine to 12 hours before the rain clears away in the afternoon."
As heavy rain sweeps into Wales, a series of flood alerts have been issued in areas such as Swansea and Carmarthenshire, where there is an increased risk of high levels of surface water.
The Met Office says heavy rain should be expected until 3pm and it could cause disruption.
This morning, Lane M4 in Wales has been closed due to flooding.
This is the route going Eastbound from J43 A465 (Llandarcy) to J42 A483 (Swansea East / Briton Ferry), although traffic is coping well WalesOnline reports.
In north Wales, the A499 near Pwllheli in Gwynedd has been closed to prepare for potential flooding.
Some residents in Devon are already being impacted by heavy flooding, with one taking to Twitter to warn others of severe flooding as a river in Dean Prior overflows.
She wrote: "Avoid this area. River overflowing and flooding at Dean prior too."
While another resident replied: "Lanes are not good at all. Be careful."
On Thursday, Brits should expect to see a continuation of cold and windy weather with sunshine and showers, along with some heavy rain in the north and west with a risk of hail and thunder.
In the East, the weather will remain mostly dry.
There will be spells of rain, occasionally heavy, pushing across most areas Friday and Saturday, while some snow is likely in the north.
The Met Office also said winds could reach speeds of up to 40 miles per hour on Saturday, December 31, while on Sunday, further rain is expected in the South.
