More than 2.5 million households have been warned they could be hit by a £116 energy bill rise this month.
Households on some tariffs will see a rise in January, with Economy 7 tariffs increasing by 7.6 per cent already in 2023.
Companies who supply those tariffs can set their own rates and were allowed to increase them on January 1 when the new Ofgem price cap was introduced.
Research from the BBC found that customers on that tariff were now paying 46% more on average than others on electricity-only tariffs.
An Economy 7 tariff measures your electricity usage based on two different prices per kilowatt; an on-peak rate and an off-peak one.
The off-peak rate applies for seven hours of the night - which is where the '7' in the name comes from - and the on-peak price applies to the other 17 hours of the day.
Energy regulator Ofgem said: “Electricity use is higher in winter for people with electric heating systems designed to use peak- and off-peak meters. This will balance out across the rest of 2023 so average bills are less than people on other meters.
"The bottom line is if Economy 7 customers use cheaper off-peak electricity for night-storage heaters, they can make substantial savings. They will pay more if they use more peak-time electricity.
“Customers have the power to switch to a new deal if it will cut their costs are rising because they don’t use electricity at night.
"Our licence requires suppliers to give customers information about the cheapest Economy 7 tariff or cheapest tariff on other meters.”
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