Britons returning to their offices today after the Christmas break faced an arctic start to the first working week of 2009.
A wave of rain, sleet and snow moved down the UK and turned to ice in many places as temperatures dropped overnight.
The Met Office issued a severe weather warning for London and east and south-east England this morning, with widespread icy roads and pavements.
Meanwhile, many people living in those areas woke to one to two centimetres of snow.
"It's going to be a bitterly cold morning," said Dan Adamson, a forecaster at MeteoGroup UK, the weather division of the Press Association.
"It's been a few years since it's been as cold as this."
December 30 saw temperatures plummet to -13C in the Scottish Highlands, while on Saturday night Benson in Oxfordshire reached -9, he said.
Though temperatures dropped below zero in most places last night, cloud cover meant it was not as cold as Saturday night.
The current cold snap is set to continue until the weekend when milder weather may finally arrive.
The chill prompted water company Severn Trent to appeal yesterday to its eight million customers across the Midlands and Wales to protect their water systems, after receiving reports that pipes were freezing even with heating on full blast.
Nikki Berry, a forecaster at MeteoGroup UK, said there were reports of snow falling overnight in many parts of the UK.
"There were snow showers in northern England. Much of East Anglia and the Midlands have had light snow," she said.
"There has also been snow in Gloucestershire and in London. But if it settles it will only be a light covering on the ground. Though it looks like Kent may see heavier snow.