A freezing spell has been forecast to tighten its grip on the country as temperatures plunge towards -10C across more of the UK.
Thermometers will fall to -10C in parts of Scotland and around -7C in southern England by dawn, causing icy havoc for millions of drivers and commuters.
But experts predict temperatures in the south will fall further to -8C or -9C overnight on Tuesday as an unusually large high pressure system continues to dominate the UK weather.
That is more than 10C below seasonal temperature norms for this time of year, which are a degree or two above freezing.
The Met Office issued a severe weather warning for London and east and south-east England on Tuesday morning with widespread icy roads and pavements.
On Monday the AA said it was braced for more than 20,000 breakdowns on what was the first day back to work for millions of workers after the Christmas break.
Brendan Jones, a forecaster at MeteoGroup UK, the weather division of the Press Association, said: "The lowest temperature so far is -10C at Aboyne in north east Scotland. Across large parts of England and Wales we will see -5 or -6C, while in the south they will go to -7C.
"But tomorrow in the South is going to be colder than tonight, with temperatures falling to -8c or -9C."
Driving conditions were made hazardous on Monday as cold east winds brought in a wave of rain, sleet and snow that turned to ice in many places as temperatures dropped overnight.
The icy conditions played a part in a fatal accident in Lincolnshire when a woman was killed after her car got stuck on a level crossing and was hit by a train.