The Met Office has issued an amber weather warning as temperatures are set to plummet across the UK.
Overnight temperatures are expected to drop to as low as -10C, increasing health risks to vulnerable people and disrupting deliveries.
The level three - or amber - cold weather alert warns of severe conditions in England between 6pm tomorrow (Wednesday 7 December) and 9am on Monday (12 December).
The alert requires social and healthcare services to take action to protect high-risk groups.
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Temperatures are expected to turn colder across much of the UK late on Wednesday and through Thursday as air from the Arctic spreads south across the country.
Met Office deputy chief meteorologist Rebekah Sherwin said: "Temperatures will start to dip this week, with daytime temperatures struggling to get above freezing in many places from mid-week onwards.
"However, the cold air from the Arctic will also bring brighter conditions, with some dry, sunny spells in many areas, particularly away from the coast.
"Showers will turn more wintry as the week goes on with a risk of snow at times.
"A yellow National Severe Weather Warning for snow has been issued for Wednesday covering northern Scotland.
"We can expect to see some snow and wintry showers further south as the week progresses, particularly in coastal areas or over higher ground. There will be widespread frosts with temperatures falling to as low as minus 10C overnight in isolated spots by the end of the week."
During the amber alert period, people are advised to tell someone when they are going out, wrap up warm and wear shoes with a good grip. You should also make sure that your home is heated to at least 18C and check in on vulnerable loved ones.
Dr Agostinho Sousa, consultant in public health medicine at the UK Health Security Agency (UKHSA), said older people and those with heart or lung conditions are particularly at risk from the cold weather, adding: "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."
Amid the cold snap, Downing Street said it was confident the UK has sufficient energy supplies to get through it.
As for whether this bitter weather means we might have a white Christmas, it's too early to say, though the Met Office has advised that temperatures look likely to rise towards the end of the month.
The long range forecast, for 20 December to 3 January, reads: "The second half of December remains uncertain, but there are hints of a return to nearer normal temperatures.
"This would be associated with spells of more unsettled weather, especially for the south, and a reducing risk of wintry hazards overall, although periods of severe weather are still possible.
"Northern areas are likely to hold onto the colder conditions for longest."
Jake Massey