Temperatures dropped to nearly minus 10C on Monday night – the coldest of the autumn so far.
According to the Met Office, the mercury fell to minus 9.9C (14.2F) in Braemar, north-east Scotland, on Monday night.
Nine of the 10 coldest locations overnight were north of the border, but the coldest location in England was Redesdale Camp in Northumberland, where the temperature was recorded at minus 7.1c (19.2F).
A yellow weather warning for dense and freezing fog was in place across large parts of England and eastern Wales on Tuesday morning.
During rush-hour, drivers from Brighton to Manchester had to contend with lower visibility and iced-up cars.
According to the Met Office, the freezing fog will "linger" across parts of England and Wales throughout the day.
Last night was the coldest night of the #Autumn so far
— Met Office (@metoffice) November 19, 2019
Meteorologist Grahame Madge said: "It's going to clear, but it might be stubborn to clear in some places, and then eager to re-form.
"We have weather warnings out until 11am (on Tuesday) but in some places it could persist more than that."
The freezing fog hung around throughout Tuesday morning's rush-hour.
North West Motorway Police tweeted to say they had received reports of a "few" accidents, adding: "the gritters have worked tirelessly all night, but it's still icy out there."
Breakdowns are more common in the winter and road conditions can be really challenging.Here's how to stay safe...Clean your windscreen inside and out.Make sure all lights are working and lenses clean.Check fuel levels. Keep at least 3mm of tread for the winter. pic.twitter.com/S5Qr15GMkZ
— North West Motorway Police (@NWmwaypolice) November 19, 2019
They also offered some safety tips for motorists, suggesting people drive on main roads, rather than quieter rural routes, and use a cigarette lighter to warm a key if the locks are frozen.
Mr Madge said: "Fog is always a driving hazard, and people need to take account of that when they are travelling."
He warned drivers not to become complacent if they have passed through a clear area, saying "Don't think the next 10 miles will be free of fog."
Temperatures throughout the day will struggle to reach double figures across much of the country.
Southampton is predicted a maximum high of 10C-11C (50F-51.8F), but only 8C (46.4F) is expected in London, 6C-8C (42.8F-46.4F) in Norwich, 5C-7C (41F-44.6F) in Nottingham, and 4C-5C (39.2F-41F) in Aberdeen.
Temperatures will fall again overnight on Tuesday, but Mr Madge could not say "whether they will drop to the levels they did last night".
He added: "We have a weather front moving in from the west that's going to stall and bring cloud and rain.
"But for the east the cold conditions are going to persist."
Public Health England has warned people to look out for others who may be vulnerable in the chilly weather.
Consultant Dr Emer O'Connell said: "Older people and those with heart and lung problems are at risk of getting sick in cold weather."