This morning, Scottish roads were mostly icy after a frosty night, with temperatures close to zero in the rest of the U.K.
Later this week, temperatures could drop down to -10 degrees Celsius (14 degrees Fahrenheit), with bitter northerly winds, according to the UK Press Association.
Fresh snow is expected on Thursday as a cold front moves south across the nation, although it may not affect the far south west.
"This will give rain initially, but it will turn to snow on its back edge," said forecaster Andy Ratcliffe of MeteoGroup, the Press Association's weather division.
According to the Met Office, the extreme weather is arriving with "an area of low pressure coming south from Iceland" and will bring back freezing conditions until the weekend and possibly beyond.
With Christmas not far away, postmen in some areas, including Yorkshire, have been forced to make special Sunday deliveries to catch up with the backlog from the previous Arctic weather.
The Royal Mail has predicted that today will be their 'busiest of the year,' according to the Daily Mail, particularly as many Christmas shoppers have taken to purchasing gifts online due to the dangerous roads and train cancellations.
"We’re working very hard, but as always we encourage people to post mail or place online orders as early as possible," a Royal Mail spokesman told the Mail.
