UK households already owe £1.3bn to their energy suppliers two months before bills rise by 80%, according to analysis.
A survey by Uswitch suggests that there are six million homes across the UK who owe an average of £206 to their energy provider.
The figure is higher than the average debt of £188 in April and comes ahead of yet another jump in energy costs in autumn.
The energy price cap is expected to be hiked to £3,582 per year for the average household from the start of October.
Further rises are also being predicted for next year, with costs climbing to £4,266 in January, before hitting £4,427 in April.
Justina Miltienyte, head of policy at Uswitch described it as an “alarming” situation.
“Energy debt has hit an all-time high with the worst possible timing, turning this winter’s energy price hike into a deeply precarious situation for many households,” she said.
“This is an alarming situation, as summer is traditionally a time when households are using less power for heating, which helps bill payers to build up energy credit ahead of the winter.”
The survey by Uswitch also showed that there are eight million households who have no credit balances, meaning they have no cushion against winter misery.
Nearly one in five people are said to be worried about their supplier forcing them to take a pre-payment meter if they fall behind on their bills.
Miltienyte underlined the need for the UK Government to take energy debt seriously ahead of winter.
“If you are behind on your bill payments, or your energy account is going into debt, speak to your provider as soon as possible,” she said.
“They should be able to help you find a solution, such as working out a more affordable payment plan.
“You may also find you are eligible for additional support such as hardship funds and other energy help schemes.
“The Government also needs to take energy debt seriously ahead of the winter – and a greater support package for vulnerable households needs to be agreed as a priority.”