Temperatures across the UK are set to plummet to as low as -10C this week with cutting Arctic winds sending a shudder down the spine of the British Isles, according to forecasters.
A high pressure system hanging over Scandinavia and western Russia is set to push raw, easterly winds towards the UK as the week progresses, causing the longest spell of cold weather so far this winter, experts say.
Snow is also forecast in some regions over the coming days with some people in Wales and the far West of England waking up to a dusting of up to 5cm this morning.
Paul Mott, forecaster with MeteoGroup, the Press Association's weather division, said: "There has been a sprinkling of snow overnight over parts of Wales, Devon, Somerset and Hampshire.
"It has mainly been over hills - with accumulations of up to 5cm in some areas - but there have also been some falls on lower ground locally.
"There will be some fairly wet snow falling over the hills of Gloucestershire, Somerset and south Wales this morning but it will struggle to settle so shouldn't cause too many transport problems."
The Met Office has issued an amber warning of snow for parts of Wales, saying the hilly parts of the south and south east of the country could get as much as 10cm.
It said higher areas of south-west England, especially Exmoor, could see 5cm of snow but lower areas are more likely to see a 1-2 cm "slushy covering".
The Met Office also issued a warning of severe cold weather across much of England until at least Thursday.
Mr Mott said the mercury could plummet to as low as -10C in rural parts of central England on Thursday night, with average day time readings only reaching 3C-4C.
"The nights will be really cold throughout the week and there will be the occasional snow shower over the eastern counties of England, eastern Scotland and even London," he added.
Police in Devon and Cornwall yesterday warned motorists in some parts of the region not to travel unless it is essential after snowfall over the higher areas of Exmoor and Dartmoor.
Gloucestershire County Council said that with bigger salt supplies than ever at this time of year it is ready for the forecast cold snap. The county's gritters were out salting the transport routes last night.
Councillor Will Windsor-Clive, cabinet member responsible for roads, said: "Even though it has been a mild winter so far we are always ready and prepared for snow and ice with a team of gritters on standby and back up teams and supervisors in each of the depots."