Rising fuel bills may force a quarter of homes to turn off their heating at some point next winter, a price comparison site claims.
Uswitch says that last winter, an estimated 20% of people it surveyed had regularly turned off their heating.
And it predicts that with fuel tariffs expected to rise, the number will be higher this year.
The Bank of England said this week that gas prices could rise by 15% later this year, and electricity by 10%.
'Pray for a mild winter'
Uswitch said that a survey of almost 1,600 of its customers carried out in January had indicated that 20% of them had turned their heating off regularly in order to save money last winter.
The firm's spokesman Ann Robinson, the former chairman of Energywatch, says: "This time it's going to be a minimum of 25%."
If the Bank of England's predictions are true, she calculates that the average British household will have to find an extra £148 over the next year.
"Many people are really going to struggle to pay their bills," she says.
"We have to pray for a mild winter."
Running out of options
At his bungalow behind the seafront in Margate, Kent, Michael Gynn has already done everything possible to cut his energy bill.
After last year's rise of just under 6%, he says he cannot afford any further increases.
He has had insulation laid in his loft, a new efficient condenser boiler fitted, along with double glazing and cavity wall insulation.
But even if the weather is cold later in the year, he knows he may now have to switch the heating off altogether.
"We've run out of options," he says. "We're now reaching the point where it's got to be turned off."
Michael works in a school art department, and does not count himself as poor.
But like millions of others, he has not had a recent pay rise, and his income is being squeezed.
"There's a lot of help out there," he says.
Prices to rise
Under recent changes, energy companies have an obligation to notify customers at least 30 days in advance of any price rises.
Centrica, the owner of British Gas, has predicted that the wholesale cost of gas could go up by 25% this winter, implying that the Bank of England's predictions might be realised.
In the meantime, the industry advises people to save energy as much as they can, and to take advantage of schemes to help vulnerable customers.
Last year, Britain's biggest energy suppliers spent £153m on programmes to give financial relief.
Christine McGourty, of industry body Energy UK, says that amount is likely to rise in the coming months.
"We would urge people who have friends or family, who they think could benefit from that, to call up their energy company and see if they're eligible, because there is a lot of help out there," she says.
For example, 250,000 pensioners benefited last year from a rebate of £80 on their bills.
Uswitch says that more than six million families are likely to be classified as "fuel poor" by the end of the year.
This prediction calls into question the government's strategy on fuel poverty, which aims to eradicate it by 2016.
By that, it means that no one should have to pay more than 10% of their take-home income on fuel bills.
But the number of people falling into that category is rising, not falling.
According to National Energy Action, there were nearly 5.5 million people in fuel poverty by the end of 2010.
Ann Robinson calculates that that figure has already risen by a quarter of a million, and may rise by another half million if the Bank of England is right about price rises.
The government is currently carrying out a review into fuel poverty, with a first report due in the Autumn.
It may decide to change the target, or even the definition of what fuel poverty means.
But in any case that report is unlikely to come soon enough to prevent millions getting cold this winter.