The BBC weather centre says December is on course to be the coldest in Britain since records began in 1910.
Christmas Day was extremely cold in much of the UK and fresh snow fell in Aberdeen, Glasgow and Edinburgh.
The Highways Agency has urged drivers to take care in difficult conditions.
However, a BBC forecaster said it would not be as cold in the next few days, although ice is likely in some areas, particularly Northern Ireland.
Temperatures fell to minus 17C at Worcester and minus 18C at Altnaharra in northern Scotland on Friday night.
The AA said Christmas Eve call-outs were 40% above normal due to Christmas shopping and the festive getaway.
It estimated that it covered about 13,000 breakdowns by the end of 24 December compared with just over 9,000 on a normal Friday.
However, British Airways said all its long-haul flights from Heathrow airport, as well as most of its short-haul services, flew as scheduled.
But some flights were cancelled from other UK airports due to the continuing bad weather in Europe.