A health warning is in place for the elderly and ailing as temperatures plummet and freezing fog disrupts travel across the country.
Public Health England (PHE) has issued its first “level three” cold weather alert since January.
It was issued after plunging temperatures hit northwest England, Yorkshire and the Humber, the Midlands and the east of England.
A level three alert is put in place when average temperatures are set to fall to 2C and if either widespread ice or heavy snow is present. A level two warning is in place for the rest of England.
Dr Thomas Waite, consultant in extreme events and health protection at Public Health England, said: “The effects of cold can be severe, in particular for those who are over 65, have a long-term illness, or are not mobile.
“Our advice to these groups is when indoors, have plenty of warm food and drinks and try to maintain indoor temperatures to at least 18C.
“Cold does kill, even in places where the temperatures aren’t at their lowest.
“Most of the practical advice on keeping warm in cold weather may seem like common sense, but it’s important that we all help each other to stay well this winter.”
On the roads, the AA urged “extreme caution” by motorists.
Spokesman Ian Crowder said: “We have got the worst possible conditions really, of fog and icy roads, and that can be lethal.”
On Wednesday a motorist was killed in a 20 vehicle crash which happened in foggy conditions on the A40 in Oxfordshire.
Fog also saw Heathrow airport hit by delays on Thursday morning while there was also a second day of disruption at London City Airport with more than a dozen flights cancelled.
Forecasters see the unsettled, milder weather over Christmas making way for clearer but colder conditions as the new year approaches.