Almost 2.5 million households already owe their energy companies an average of £120 as winter begins, according to a survey.
Households collectively owe energy providers £292 million at a point in the year when they should be in credit in preparation for the expensive winter months, the poll for uSwitch found.
Some 40% of those in debt said they were increasing their monthly payments to pay off their debts but almost a fifth (18%) said they were ignoring the situation in the hope the debt would disappear over time.
Ofgem figures indicate that 70% of annual household gas and 54% of household electricity use occurs between October and March.
Wholesale prices, which make up around half of energy bills, have continued to rise due to the low value of the pound pushing up the cost of energy imports, future supply concerns and higher transmission prices.
Uswitch energy spokeswoman Claire Osborne said: "These new figures show how unaffordable energy is for hard-pressed consumers. Winter has barely begun, yet millions of households already owe significant sums to suppliers.
"Once the cold weather really starts to bite, some consumers will inevitably find themselves in further financial difficulties.
She added: "If you are in debt, ignoring it won't make it go away. Your first port of call should be speaking to your energy supplier to discuss the problem and work out ways to help resolve it."