Millions of people are borrowing to pay essential bills at Christmas, charities warn, with energy debts a key concern as prices are set to rise again.
Citizens Advice said it was seeing more people falling behind on energy bills as winter began, owing an average of £1,841 to their supplier.
Charities say some families face paying off loans, adding to the financial strain as they cut back on basics.
The Joseph Rowntree Foundation, which campaigns on social issues, said a third of those it surveyed said they still had loans to pay off, which had originally been taken out to cover the costs of food, housing costs, energy bills or council tax.
Those debts can grow as interest is added, but there are warnings that people are still borrowing to make ends meet.
Debt charity StepChange estimated that 2.6 million UK adults used credit to pay for essential household bills in the last three months. Nearly half of those with existing debt faced difficulty keeping up with household bills and credit commitments.
New figures from Ofgem, the energy industry watchdog, revealed that the amount of debt and arrears faced by gas and electricity customers swelled to £2.9bn between July and September.
That is up from £1.9bn in the same three months last year and 13% higher than the previous quarter between April and June.
Households in arrears – where a customer owes a supplier but has not worked out a payment plan – make up the vast majority of the overall figure, at more than £2bn.
Customers in debt, who have a re-payment agreement with their energy company, totalled £830m.