A new low in customer satisfaction with gas and electricity suppliers has revealed "the failings of a broken energy market", according to consumer group Which?
The watchdog's latest annual energy company survey found that the overall customer satisfaction score has dropped from 49% last year to 41%.
The score is one of the lowest recorded by Which? from all of its satisfaction surveys across a range of products and sectors.
The consumer group said the survey exposed a market "that is falling short of its customers' needs" as satisfaction plummeted and the biggest companies fared worse than the smaller suppliers.
The six largest companies, which account for more than 90% of the market, ranked bottom of the table, with Npower scoring the lowest for the third year running with 31%.
British Gas scored 39%, below SSE and Scottish Power on 41%, EDF Energy (44%) and E.On (45%).
British Gas and Npower both fell below the industry average of 41%.
Good Energy held the top spot for the third year running, sharing it with Ecotricity, with both scoring 82%.
All of the companies that appeared on the table last year scored lower, except for Ecotricity and First Utility who have risen from 80% to 82% and 50% to 58% respectively.
Latest statistics from Which? show that energy prices are the top worry for 84% of consumers, while just 20% trust suppliers to act in their best interests.
Some 60% of consumers told Which? that they are already "dreading" the cost of their winter energy bill.
Which? executive director Richard Lloyd said: "Once again the biggest energy companies have been beaten by the smaller suppliers but there are no winners in a broken market that consistently fails consumers.
"Our findings highlight why it's vital that Ofgem's first annual review of competition clearly identifies why the market is failing and what needs to change.
"We want to see radical solutions to improve competition and keep prices in check, like the biggest energy companies being forced to separate wholesale generation from the retail arms of their business."
Npower's director of domestic retail business, Roger Hattam, said: "We know we've let many of our customers down following recent issues with our new billing system but it's still disappointing to see these results.
"Right now, our priority is to put right these issues. While we still have a long way to go, we are making progress. Our customers deserve to get the best service possible and this is my commitment to them."
Shadow energy and climate change secretary Caroline Flint said: "These figures are a damning indictment of a broken energy market that is failing to meet the needs of consumers.
"Under David Cameron people are paying more than ever for their gas and electricity, but all too often the customer service they receive is not good enough.
"That's why the next Labour government will undertake the biggest overhaul of our energy market since privatisation.
"Our plans will break up the big energy companies, put an end to their secret deals and make tariffs simpler and fairer.
"And until these reforms kick in, we will put a stop to unfair price rises by freezing energy bills until 2017, saving the average household £120."
An Energy UK spokesman said: "Major change is already under way in the energy industry and will ensure dealing well with customers is at the heart of what our members do.
"Companies put a very high value on the relationships they have with their customers and they are working hard to improve the service they provide.
"However, in any survey there will always be winners and losers with someone at the top and the bottom.
"Examples of best practice set a bench mark for all companies to meet and, where issues are highlighted, serve as a wake-up call for everyone.
"Around a million people shopped around for a new energy deal or provider in November and December proving there are good offers out there and that the market is dynamic and working well for consumers."
:: Which? surveyed 8,525 UK energy bill-paying adults in October and November.