Energy companies were today urged to improve their complaint handling procedures after the regulator Ofgem said one in four customers were unhappy with how their grievances were dealt with.

Ofgem said there were “low levels” of satisfaction across all suppliers - with billing and prices the most common grievance - but added some performed better than others.

Scottish and Southern Energy and E.ON rated joint highest with 29 per cent of customers satisfied, while npower was lowest with 16 per cent. Scottish Power recorded 24 per cent, while Centrica and EDF Energy each polled 20 per cent in the survey of 2,700 customers.

Common gripes included the number of times they had to contact the supplier, the attitude of staff and a failure to return calls.

In a letter sent to bosses of each of the major energy companies today, Ofgem chief executive Alistair Buchanan said: “It is in suppliers’ best interests to ensure that the service they provide is of a high standard. This is clearly an opportunity for them to raise the bar to retain existing customers and attract new ones.

“With the systems and processes in place, the challenge now for companies was to really listen to what their customers were saying and look at how they could address their concerns.”

There have also been calls to improve the billing process after a seperate survey claimed that energy bills are so confusing that they could lead to customers falling into debt.

Three quarters of respondents to the survey by Uswitch, the comparison website, said energy bills were complicated. Around 40 per cent saying they were unable to work out how their bills were calculated using the information on their statement.

The research also found that nearly two out of three consumers found their home telephone and water bills confusing. In contrast, bank, council tax and credit card statements, are the most easily understood.

Uswitch says that the energy industry is lagging behind other sectors in communicating simply and clearly with customers and that the lack of clarity leaves some consumers vulnerable to being overcharged.

Last week, the consumer watchdog, Consumer Focus, accused suppliers of overcharging customers by as much as £1.6 billion, or £74 per household, for failing to pass on drops in wholesale energy prices.

Ofgem, the energy regulator, denies this, after clearing suppliers of profiteering from wholesale price fluctuations in its last quarterly review of the industry.

However, consumer groups say the need for greater clarity on energy pricing is needed, especially as domestic energy costs are set to soar in the next few years.

Currently, domestic energy bills cost about £1,250 a year for dual fuel. However, this is set to quadruple within the next 10 years, according to Uswitch's analysis of current pricing trends.

Ann Robinson, energy expert at Uswitch said: "A well-written, clear and concise bill should leave consumers feeling empowered and in control, not bemused. This is why it is so worrying to find that three quarters of us are confused by our energy bills."

Peter Jenkins of the Energy Retail Association, which represents energy suppliers, said: “The industry sends out 200 million energy bills to customers each year. It is in the interests of energy suppliers to ensure that bills are as straightforward and easy as possible for customers to understand.

"This is why energy suppliers are working with Ofgem, the regulator to make sure customers have as much information as they need on their energy bills in order to make informed choices about their energy usage.”