British Gas has been voted the UK's worst company for dealing with customer complaints.
Gas and electricity providers in general have been hit by a series of mis-selling scandals, with thousands of customers having been duped into switching energy supplier or complaining of heavy-handed salesmen.
And in March, British Gas was singled out for criticism by consumer group Energywatch for increasing prices for its 13 million domestic customers.
Paradoxically, in the nationwide survey of 2,900 consumers, British Gas was also voted seventh best firm overall for levels of customer service.
British Gas said: "We recognise that good complaints handling can turn complainants into advocates and build customer loyalty. So, we're both pleased and disappointed by this puzzling survey."
Marks & Spencer came top of the customer complaint handling table, perhaps completing the former High Street favourite's rehabilitation after a troubled few years.
The survey also revealed that customers want more personal
communication, presenting a dilemma for companies wanting to drive down costs.
Many of those surveyed defined good service as "getting through to a real person first time".
As for call centres, the survey concludes that hard-pressed staff are hindered by lack of training and support from their employers.
The National Complaints Culture Survey, carried out for Time Manager International, suggested that Britons were becoming more likely to complain, although only 16% said they complained every time they were dissatisfied.
Londoners were the most likely to gripe, with 60% saying they complained most of the time when they were dissatisfied.
The least likely to complain were the Welsh - only 40% said they complained most of the time.
The survey concludes that UK customers are "increasingly frustrated with how their complaints are handled as their expectations of quality service increase".