Weather forecasters are warning of snow, blizzards and freezing winds for later this week.
Snow in store for some regions
After a weekend where some parts of the country felt more like spring than winter, the icy cold blast could come as quite a shock.
Freezing cold air will rush in from the Arctic, bringing icy conditions for much of the country and sending park joggers running for cover.
And all that will be preceded by a howler of a day on Thursday.
Sky weather forecaster Denise Nurse said sub-zero temperatures would bite across Britain.
"We're going to see snow across the country.
"The wintery spell will start on Thursday with a big storm, and then Friday and into the weekend will get very cold.
"But there will be some lovely clear skies and crisp days while it is cold."
Sky's Denise Nurse
Blizzards are expected across northern Scotland and the Northern Isles later on Thursday night and right through Friday with deep snow and substantial drifting looking likely.
This January has so far proved exceptionally mild. Maximum temperatures today are expected to reach 12C in London, 11C in Manchester and 9C in Edinburgh.
But by Friday the temperature in Scotland could be struggling below the OC mark and down to as low as 1C in England and Wales.
For those who do not like the cold, however, the good news is that mild weather is expected to return next week.
METOFFICE WARNING: Scotland, Wales and North East England of up to 10cm of snow and 20cm on higher grounds.