The energy watchdog Ofgem has launched an investigation into the number of struggling households forced onto expensive prepayment meters.
Ofgem could land suppliers with fines if it discovers wrongdoing by the firms.
The probe came after Business Secretary Grant Shapps, who wrote to Ofgem, warned energy suppliers could be named and shamed.
It comes amid mounting concern about the number of households being forced to have a prepayment meter, often to recover debts.
However, with energy bill prices soaring and prepayment meter rates higher than other ways of paying, there is evidence that some households are going without heating and lighting altogether.
Analysis shows courts are waving through suppliers’ applications to install prepayment meters.
Jonathan Brearley, Ofgem chief executive, said: “I am concerned about the sharp growth in households struggling to pay their bills being switched over to prepayment meters, sometimes without their even knowing about it, leaving them without heating.
“I have spoken to many customers including those who use prepayment meters.
“Many families choose this as an option principally to have more control over their budgets.
“And used responsibly, they strike the right balance between protecting customers from being cut off and enabling suppliers to recoup debt.
“However, I have heard directly from people who have faced poor practice from suppliers. “For example, one customer I spoke to in Glasgow left to go on holiday and returned to find he’d been switched to prepay without his knowledge and had no way to top up.”
Gillian Cooper, head of energy policy for the charity Citizens Advice, said: “We welcome the government’s call for energy suppliers to stop forcing people onto prepayment meters.
“Millions of people are being left in cold, dark and damp homes because they can’t afford to top up their meter. No one should be forced to live like this.
“It’s now up to suppliers to do the right thing and end this practice. "If they don’t, the government must step in with stronger action.
“It’s also vital further protections are brought in for people already using prepayment meters.”
