As the UK braces for sub-zero conditions, Public Health England says it is a good time to check on vulnerable people.
Winter is set to bite this week with temperatures falling away to a possible low of -8C (17.6F) on Thursday and authorities issuing a health warning.
Snow is expected to fall in hilly areas of the country and parts of Scotland could even see -10C (14F).
The Met Office forecast comes after the UK experienced bitter temperatures at the weekend, but stayed above freezing for most.
On Sunday night, some isolated areas experienced sub-zero conditions, such as Cairnwell in the Scottish Highlands.
Cloud and rain in the south means temperatures have now risen to between 8C and 9C.
But forecaster Helen Roberts said it would become increasingly cold as the week progresses.
“A return to cold is the theme for this week – cold, breezy with a return of widespread overnight frost and wintry showers predominantly around the coastal fringes of the UK,” she said.
“Thursday is looking like it might be the coldest day and night of the week.
“We will potentially have some lying snow across the hills of Scotland and northern England and that always helps to keep temperatures down.
“So we could potentially see temperatures as low as -8C, possibly minus 10C, across parts of Scotland where there is lying snow by Thursday night.
“And even across England and Wales we could see -6C to -8C and some snow across hillier parts.”
Sky News weather producer Christopher England added that it would likely remain cold through next week as well, and Public Health England (PHE) has issued a cold weather alert and health warning.
Dr Thomas Waite, of PHE’s Extreme Events team, said: “As the weather is going to get colder everywhere in the coming days, this is a really good time to check on those who may be at risk.
“People with diseases such as heart and lung conditions, older people, and young children can feel the ill-effects of cold weather more than the rest of us.”
South Western Railway warned commuters the adverse weather conditions could affect journeys.
“Ice can cause problems for trains as it can prevent trains from drawing power from the electrified rail,” said a statement on its website.
“Network Rail-run special vehicles treat our tracks to reduce the effects of the poor weather conditions and will be taking appropriate action over the next few days.”