Snow, ice and freezing fog that is sweeping across parts of the UK will continue for days, forecasters said.
The conditions have caused travel disruption, with delayed trains, motorway accidents and flights from Heathrow cancelled on Sunday morning.
A number of people are in critical condition after being pulled from a lake amid freezing temperatures in Solihull, according to police.
Temperatures could drop as low as -15C (5F) in northeast Scotland overnight.
If so, it would be the lowest temperature the UK has seen since February last year.
BBC weather presenter Darren Bett said: "It looks set to stay very cold for the week ahead. Snow and ice, as well as freezing fog, will continue to be a hazard and frosts will continue to be widespread and severe.
"From Tuesday, the cold northerly wind will develop and bring most of the snow to northern Scotland with as much as 20cm (7.8in) of fresh snow falling in the hills."
Earlier, the Met Office warned power cuts and mobile phone coverage might also be affected.
Snow has been settling in Devon and Wales as well as parts of Scotland and areas of north-west England.
A yellow weather warning for snow and ice is in place for Scotland, London and south-west England until Monday morning.
But the Met Office ended its weather warning for Northern Ireland, despite the cold weather leading to some sporting fixtures being cancelled.
Heavy snowfall caused a series of traffic collisions on Sunday, leaving drivers in treacherous conditions.
In Shropshire, the M54 between junctions 3 and 2 was shut, while major congestion was also reported on the M5 slip road to the M6.
The southbound M5 in Gloucestershire was shut after a multi-vehicle crash between junctions 11A and 12 near Quedgeley, Highways England said.
Drivers in north-west England were also being advised to take care following accidents on other motorways including the M58, M62, M61.
Trains across the West Midlands have also been hit by delays.
Heathrow Airport confirmed scores of flights were cancelled on Sunday morning due to the fog.
On Saturday, Manchester Airport closed both runways due to "heavy snow fall", with dozens of flights affected.
Met Office chief meteorologist Steve Willington said: "It is staying cold with daytime temperatures remaining only a few degrees above freezing in many places over the coming days and overnight temperatures dropping to -10C or lower in isolated spots.
"Although below average, these temperatures are not that unusual for this time of year.
"There is still a risk we could see some freezing fog in places particularly southern England."
People are being advised to check on vulnerable family and friends to ensure they have access to warm food and drinks as the wintry conditions hit.
The UKHSA added that people should make sure indoor temperatures in their homes are at least 18C.
Dr Agostinho Sousa, consultant in public health medicine at UKHSA, said: "Cold weather can have serious consequences for health and older people and those with heart or lung conditions can be particularly at risk.
"If you have a pre-existing medical condition, you should heat your home to a temperature that is comfortable for you.
"In rooms you mostly use such as the living room or bedroom, try to heat them to at least 18C if you can. Keep your bedroom windows closed at night. Wearing several layers of clothing will keep you warmer than one thicker layer."
Gritters will be out this weekend to help clear the roads and ease travel disruption.
Darren Clark, severe weather resilience manager at National Highways, said: "National Highways is committed to treating every road which needs to be treated - whenever it is needed."
The RAC has added it has been "exceptionally busy" in recent days due to receiving a quarter more breakdowns than is normal for this time of year.
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2022-12-11 15:28:55Z
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