Millions of energy customers have been urged to switch suppliers or at least tariffs to save more than £400 a year before the latest round of price hikes comes into effect.
Some nine million customers of the Big Six companies should switch to a better deal or end up overpaying by up to £434, Which? has warned.
The latest price hike by British Gas came into effect on May 29, increasing the bills of four million of its dual fuel standard tariff customers from £1,101 to £1,161 – 5.5% or £60 – on average per year.
The amount is £364 more than the cheapest deal on the market, but still only makes the British Gas standard tariff the fourth most expensive of the Big Six firms after npower, Scottish Power and SSE once all price rises have come into effect, the watchdog calculated.
SSE customers on its standard tariff will see the biggest price increase at an average £76 more per year.
The firm announced a 6.7% price rise this week to come into force on July 11, meaning customers will pay £1,196 per year on average.
Overall, npower customers will pay the most as its 5.5% price increase will mean customers on its standard tariff will pay £1,230 per year on average from June 17.
Which? said npower customers on its standard tariff could save up to £434 by switching to the cheapest deal on the market, Utility Point’s variable tariff at £797 per year, or £268 by switching to npower’s own cheapest tariff.
British Gas households who want to remain with the supplier could save £113 if they transferred from the standard tariff to the best deal available.
Scottish Power customers on its standard tariff will see their bills increase by an average of £63 a year under a 5.5% increase coming into effect on June 1, bringing its standard tariff to £1,211 on average per year.
The one million households on this deal will be paying £414 more than if they were on the cheapest deal on the market and £100 more than Scottish Power’s own cheapest tariff, the consumer group calculated.
Over a million EDF customers on the firm’s standard tariff will see their electricity bills increase by 1.4%, or £16 a year, from June 7, taking the deal to a total of £1,158 for the average user – £361 more than the cheapest deal on the market and £167 more than EDF’s own cheapest deal.
E.On has not announced a price increase but announced in March that it was cutting dual-fuel and paperless discounts from its bills and increasing its standing charge for some customers.
The watchdog said this would mean some customers paying £30 more a year, leading to an average annual bill of £1,153.
Companies have blamed rising policy, network and wholesale energy costs for the price increases.
Alex Neill, Which? managing director of home products and services, said: “Before the energy price cap comes into effect later this year, anyone still suffering on a poor value standard tariff should take five minutes to compare and switch as they could potentially save up to £434 a year.”
Energy Minister Claire Perry said: “Eleven million households are already paying far more for their energy than they need to which is why we took the unprecedented step of introducing legislation to put a cap on prices for those on the most expensive default tariffs.
“It is extremely disappointing that SSE has decided to announce this unjustified price rise, the highest yet from the Big Six, ahead of the new law coming into effect later this year.
“Consumers should vote with their feet. Switching suppliers will always help consumers get the best deal.