People face “terrible consequences”, a charity has warned, as parts of the UK face plummeting temperatures.
The Met Office has issued several yellow weather warnings for snow and ice over the next few days, and the UK’s Health Safety Agency has also issued a level three cold weather alert covering England.
Get the five-day forecast where you live
National Energy Action said more government support is needed for “those most at risk” in the freezing conditions.
Adam Scorer, chief executive of the charity, said: “Impossible high prices and now the cold weather will mean millions of people struggle to stay warm and safe at home.
“Our figures show that 6.7 million UK households are fuel poor after energy prices almost doubled in a year.
“We hear daily from people who are forced to turn off the heating when they need it most.
“The vicious choice is huge debt or a house without heating, with dire consequences either way.
“Now we’re going to start seeing how sad this winter is going to be.”
Read more: Winter payments unleashed as UK hit by Arctic blast Families face tough decisions after year of cost-of-living crisis
The Met Office has issued a yellow ice warning covering northern England, the west and east coasts of England, the coast of Wales and the northern part of Northern Ireland on Friday.
A yellow warning for ice and snow is in place for most of Scotland, which continues on Saturday and Sunday.
Image: Met Office warnings across the UK
Also on Saturday, a yellow ice warning is in place for northern Northern Ireland and the western side of the UK, including the coast of Wales and Cornwall.
Temperatures were expected to drop to -10C overnight on Friday, and roads, cycle paths and pavements could be icy, the Met Office said.
Image: A light dusting of snow in the Brecon Beacons on Wednesday. Image: AP Image: Dressing warmly in London on Thursday
Low temperatures led to winter chill payments for some postcodes in England and Wales.
This means people on low incomes receive a payment of £25 if the average temperature in their area has been (or is predicted to be) 0°C or below for seven consecutive days.
Use the Chrome browser for a more accessible video player
2:35 Millions cannot heat their homes
The Department for Work and Pensions said these payments could be activated until the end of March.
A spokesman added: “We are committed to protecting the most vulnerable in our society and this extra help is on top of wider government support which includes £1,200 in direct payments already issued to millions of low-income households this year.
Use the Chrome browser for a more accessible video player
0:30 Arctic blast brings snow to Scotland Image: Rosslyn Chapel in Edinburgh on Thursday
“On top of this, we’re offering households £400 off their energy bills this winter, with our Energy Price Guarantee saving the typical household an extra £900.”
Meanwhile, The Daily Telegraph has reported a warning from National Grid that electricity supplies will be tight on Friday and Sunday due to the cold weather.
The network said it may have to use “enhanced actions”, which the Telegraph said include a new scheme where households are paid to use less electricity to ease pressure on the supply.