Up to four inches of snow could fall in London and southeast England as an arctic blast sends temperatures tumbling to as low as -15C in Scotland.
The Met Office has issued a yellow snow and ice warning for southern and eastern England from 9am on Sunday to 9am on Monday, warning of widespread disruption with a "slight chance" that rural communities could be cut off.
The warning, which lasts for 24 hours, says two to five centimetres of snow could fall quite widely and up to 10cm (four inches) in places.
It was issued after identical warnings in other parts of the country.
The Met Office said: "Snow may push in across parts of east and southeast England, leading to a risk of travel disruption especially on Monday morning."
Spokesman Grahame Madge added: "The outlook for the UK remains cold at least for the next seven days, with the potential for this to continue even longer."
Temperatures dropped as low as -9C (15F) in Benson, South Oxfordshire, overnight, and Sky News weather producer Joanna Robinson said -15C (5F) could possibly be reached in Scotland where there is snowfall and clear skies over the coming week.
The Met Office had already issued several yellow weather warnings for snow and ice which are in place for parts of Scotland, Northern Ireland, Wales and South West England.
In addition, the UK Health Security Agency (UKHSA) has issued a level three cold weather alert covering England until Monday - as a charity warned the worsening cold snap could bring "dreadful consequences" with millions unable to afford to heat their homes.
The health body advises vulnerable people to heat their homes to at least 18C, wear extra layers of clothing, and eat hot food to protect themselves.
As parts of the UK are hit by freezing conditions, those on the lowest incomes in England and Wales will receive a £25 cold weather payment.
The winter payments are triggered for eligible households where the average temperature has been or is forecast to be 0C or below over a period of seven consecutive days.
Robinson said further wintry showers into next week will bring icy stretches, with conditions reaching well below freezing.
She said: "The Arctic air is across us now, bringing wintry hazards that could last for most of next week, but there will be plenty of sunshine.
"Like recently, temperatures will widely drop below freezing at night, reaching -4C to -8C under clear skies, and -10C is likely in some prone cold spots.
"Where there's snow cover, mainly in Scotland, clear skies could bring lows close to -15C.
"And it's staying cold in the day, with temperatures generally 2C to 4C, but freezing in some places.
"Disruptive freezing fog is looking increasingly likely over the weekend, especially in the south."
The Met Office has extended a yellow weather warning for snow and ice in northern Scotland until 12pm on Sunday.
It warned some disruption is likely due to icy surfaces in coastal and northern England and parts of Wales and Northern Ireland where yellow warnings for ice were issued for Friday.
The icy conditions in coastal England and parts of Northern Ireland and Wales are expected to continue into Saturday.
The forecaster's meteorologist Alex Deakin said earlier this week there was a potential for "significant" snow in parts of England and Wales in a predicted weather model for next week, which shows a low pressure system heading towards the UK.
He added: "The weather patterns don't shift too much by the time we get to Monday, we've still got the cold air in place, cold weather fronts around, some freezing fog and some ice as well."