Thousands of households which use smart meters and are in debt on their energy bills are being moved over to a prepay method which costs more and could leave them cut-off.
Data from Ofgem show that around 60,000 UK households have already had their meters remotely switched to prepayment mode over the last three months.
This can be done without the permission or consent of a homeowner, and once in prepayment mode people will have to pay higher rates and could face disconnection.
It is a similar concept to a pay-as-you-go phone contract and the rates you will pay cost more than those on a direct debit.
Speaking to the the BBC, Ofgem has said that it received reports of: "vulnerable customers being left without power for days or even weeks."
Ofgem's rules state that energy companies need to speak with customers before moving them on to a prepayment meter, but the regulator told the broadcaster it was concerned this was not always happening.
Customers are moved to prepay meters to stop them from accruing debt which they can not feasibly pay back.
Last year more than 152,000 households with smart meters were remotely switched to more expensive prepayment plans for gas or electricity, according to Ofgem figures
Citizens Advice recently found that some 450,000 people could be made to pay their energy bills with a prepayment meter by the end of the year.
Dame Clare Moriarty, Chief Executive of Citizens Advice, said: "Energy companies have a duty to protect customers, but forcibly moving people in debt onto prepayment meters is disconnection by the backdoor.
"Even with the bill freeze in place, the cost of energy will still be at a record high. If people can’t afford to top up, they’re at real risk of the heating going off and the lights going out.
"The Government must bring in a winter ban to stop energy companies forcing people already struggling onto prepayment meters.
"It should also bring in targeted support to help people on the lowest incomes pay their bills."
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