Plummeting temperatures have prompted public health chiefs to warn the elderly to keep their homes warm and have the flu jab.
The Met Office has warned winter has begun to bite after an unseasonably warm December, with large parts of the UK facing blasts of snow, ice and frost.
Yellow warnings for ice have been issued for Northern Ireland, Scotland and parts of north Wales and north-west England as the mercury falls below zero.
A widespread frost is expected across the country on Wednesday morning with temperatures reaching as low as minus 5C in parts of Scotland overnight, according to MeteoGroup.
Officials have urged families to help protect their relatives from the cold snap.
Public Health England's Dr Angie Bone said: "Over the past few weeks we've had some very disruptive weather, but temperatures have been quite mild - now the weather will be colder over much of the country, which will be a significant change.
"It's so important to remember that cold does kill, even in places where the temperatures aren't at their lowest. Most of our advice at PHE on keeping warm in cold weather may seem like common sense but people should think about how the cold weather can affect them."
People, particularly the elderly and those with illnesses, should heat their homes to at least 18C, have hot drinks and if eligible, get the flu vaccination, she added.
Official figures showed winter deaths jumped by 151% last year, with an estimated 43,900 excess deaths in England and Wales between December 2014 and March 2015.
An less-than-effective flu jab and cold weather were said to be major factors.
Charity Independent Age is offering free advice to elderly people and their families to beat the chill.
Lucy Harmer, director of services at Independent Age, said: "Winter can be a testing time for many elderly people if they don't have enough social, financial or emotional support in place. We would urge older people, their families and carers to take extra care during the cold snap.
"The Government, councils and individuals all need to take more responsibility for ensuring older people are getting the support they need in winter."
The cold front is set to remain into the weekend, with Scotland and northern England bearing the brunt of the wintry weather.
John Lee, a forecaster at MeteoGroup, said: "The showers mostly cleared away by daybreak and it will be cold and clear in most places. There will be a widespread frost and minimum temperatures overnight could get as low as minus 4C or 5C in Scotland.
"There will be snow across southern Scotland and northern England, which could be quite heavy at times, especially during the night.
"Over the next few days temperatures are unlikely to get much higher than 5C or 6C pretty much anywhere and we are likely to see more widespread frost."
The cold snap is in sharp contrast to last month, which was both the wettest and warmest December on record, when temperatures averaged 7.9C (46.2F).