The new year has been ushered in by widespread frost and freezing fog with temperatures plunging below freezing after midnight.
Temperatures dropped as low as minus 4C in some parts of southern England in the early hours, and wintry showers are expected across north-eastern Scotland and the north-east of England, according to the Met Office.
Forecaster Clare Nasir said: “It’s going to be a bitterly cold start to the new year across southern areas and quite murky as that fog lingers on.
“It’s going to be a cold day, particularly in the South where we’re not likely to see the sunshine.
“Brighter skies in western Scotland, the central belt, down towards the North West of England, and sheltered spots of Northern Ireland as well as Wales seeing some brighter skies.”
A yellow warning for ice, issued on New Year’s Eve and covering the majority of Devon and Cornwall, remained in force until 9am.
A New Year’s Eve ice warning covering the majority of Devon and Cornwall, for motorists on the M5 facing standstill conditions, remains in force until 9am.
Some 23 flood warnings – meaning flooding is expected and imminent action is required – were in force in patches across southern and south-east England.
Over the weekend, the cold spell will continue with “locally severe overnight frosts, especially across the North”, the Met Office said, adding there will be some wintry showers across eastern parts.
Police forces in areas hit by ice and snow urged motorists to travel only if necessary as crews attended several collisions.
RAC Breakdown spokesman Simon Williams said: “We strongly urge drivers to exercise caution on New Year’s Day with a high risk of both snow and ice on the roads.
“The message for those who have to drive is to adjust their speed according to the conditions and leave extra stopping distance so 2021 doesn’t begin with an unwelcome bump and an insurance claim.
“Snow and ice are by far the toughest driving conditions, so if they can be avoided that’s probably the best policy.”
It comes after the final day of 2020 brought bitterly cold conditions for much of the UK and more snow – with a low of minus 7.5C recorded in Topcliffe, near Thirsk in North Yorkshire.