Which? urged the £10 million consumers who have their energy supplied by the six major firms - including Glasgow-based Scottish Power and Perth-based SSE - to shop around for the best deal.
From tomorrow, the price cap on standard and default tariffs will be set at £1,254 per year for a medium dual-fuel customer paying by direct debit – £34 more than companies were charging in December when the cap was brought in and adding £117 to the average bill.. It applies only to default tariffs rather than fixed deals.
Natalie Hitchins, Which? head of home products and services, said: “Many people who hoped the price cap would bring an end to unwelcome price increases will be left reeling after price hike Monday adds more than one billion pounds to their energy bills.
“If you are one of the millions of energy customers stuck on a rip-off standard variable or default tariff, our advice is simple - switch as soon as possible. There has been a recent rise in the number of cheap deals on the market - so you could choose better customer service while potentially saving more than £300 a year.”
Recent Which? research showed there are now more than 30 energy deals priced at under £1,000 a year - up from just eight in December 2018. However, a number of smaller suppliers have collapsed in recent months - including Selkirk-based Spark Energy, which folded in January, citing rising wholesale costs and tough competition.
Stephen Murray, energy expert at MoneySuperMarket, said: “This price rise might sound like an April fool, but unfortunately it’s no laughing matter. If you’re one of the 11 million people already paying too much for your energy, by the time Monday comes around your bill could make for unpleasant reading."