More than half a million households have fallen behind on their energy bills since February, taking the total number of billpayers in arrears to more than 2 million.
Citizens Advice said an extra 600,000 households owed payments to their energy suppliers, with the coronavirus outbreak leading to record high redundancies this year.
On average, billpayers who have fallen behind on their payments owe their energy suppliers about £760 for electricity and £605 for gas, according to Citizens Advice.
The findings show that about 16% of homes that use energy prepay meters – or almost 700,000 households – have not been able to afford a top-up since March.
Citizens Advice warned that financial woes were likely to deepen through the colder months and that an estimated 7 million households were expected to struggle to pay their winter energy bills this year.
Alistair Cromwell, the acting chief executive of Citizens Advice, said: “We’re heading into the coldest months of the year and the full financial impacts of the pandemic are still to be felt.”