Millions of people will be struggling to stay warm, a charity has warned – as parts of the UK are set to be hit with snow and freezing conditions.
National Energy Action said people faced a "vicious choice" between a cold home and falling into debt.
Temperatures are set to drop below zero overnight and could reach -10C (14F) in rural areas, the Met Office said.
Four yellow weather warnings for snow and ice are in place across the UK from now and over the weekend.
Snow has already fallen in parts of Scotland and northern England, and forecasters are predicting snow for London, the South East and East of England on Sunday.
BBC Weather's Sarah Keith-Lucas said the cold snap was going to "stay with us for at least the next week or so, so there is no let up in these very low temperatures".
Friday night into Saturday will see "sharp frosts, some snow flurries and some icy conditions as well as some fog", she said, with the potential for snow showers in some parts.
Ms Keith-Lucas added that overnight temperatures would widely drop to -4C and -6C, although temperatures could fall even lower in some places.
Sunday will be another cold day, she added, "with the potential for some sleet and snow in the south east" of England.
The Met Office's four yellow weather warnings include:
The UK Health Security Agency has also issued a level three cold weather alert covering England until Monday.
In Scotland, the Met Office said temperatures are set to drop below zero overnight and could reach -10C (14F) in rural areas – with up to 5cm of snow at lower levels.
Heavy snow has already caused traffic disruption across the north east of Scotland, with reports of vehicles becoming stuck on some routes.
Network Rail said a normal train service was planned across Scotland, but with cold temperatures expected into next week, a meeting would be held to go over the weather forecast.
Adam Scorer, chief executive of fuel poverty charity National Energy Action – which works across England, Wales and Northern Ireland – warned people were being forced to turn their heating off.
The charity called for the government to do more to help "those at greatest peril" stay warm.
People on the lowest incomes in many parts of England and Wales are set to receive a £25 Cold Weather Payment. The system is different in Scotland, where those on low incomes and benefits may receive the Winter Heating Payment.
The Met Office warned the wintry conditions could continue over the next seven days.
Met Office spokesman Grahame Madge said: "Along with the cold air there are a number of weather-related hazards including freezing fog, especially for Sunday and Monday mornings in the south of England.
"Overnight temperatures are likely to dip widely below zero with some more sheltered spots dropping to -10C.
"Our forecasters are looking at the possibility of snow affecting the south-east of England on Sunday night and into Monday morning. If this happens it could bring some disruption to Monday's rush hour."
How have you been affected by the cold snap? Email: haveyoursay@bbc.co.uk.
Please include a contact number if you are willing to speak to a BBC journalist. You can also get in touch in the following ways:
If you are reading this page and can't see the form you can email us at HaveYourSay@bbc.co.uk. Please include your name, age and location with any submission.
How long will the cold snap last?
Coldest night of 2022 as Scots struggle with bills
Met Office extends wintry weather warning
What's the cheapest way to keep warm? Your questions answered
Warnings or alerts: what is the difference?
Who will get a Cold Weather Payment this week?
Stansted suspends all flights due to bad weather
Shooting of three women at cafe shocks Italy
'They beat my son for refusing to fight in Ukraine'
'They beat my son for refusing to fight in Ukraine'
They are K-pop's next stars… and they’re entirely virtual
The themes of two unexpected World Cup semi-finals
Check out the World Cup schedule
The secret diaries of women protesting in Iran. Video
One of Central America's most active volcanoes erupts. Video
What was Genghis Khan’s ‘secret weapon’ on the battlefield?
'We witnessed history as Morocco won'
'Brutal – this England exit is even more painful'
The French breakfast you don't know
The rise of the remote helicopter boss
The underwater sounds that can kill
© 2022 BBC. The BBC is not responsible for the content of external sites. Read about our approach to external linking.
