Domestic customers are facing rising power bills

About 5 million London Energy, Seeboard Energy, SWEB Energy and Virgin Home Energy customers will see bills go up.

EDF blamed the increase, of 3.5% in gas bills and 3.8% in electricity bills from 13 September, on wholesale prices.

But Energywatch said households should not accept continual rises "without good reason".

Domestic customers of EDF and its trading companies, which are concentrated in the South East of England, saw gas bills increase by 4.6% and electricity bills by 6.7% in March.

In September household bills for typical gas customers will go up by about 19p a week. Electricity customers will see an average rise of 24p a week.

Blaming the markets

EDF Energy said the move follows similar rises by its competitors.

But Energywatch, an independent consumer watchdog, said that repeated rises in energy costs should not be accepted "without question".

"One after another, energy companies are increasing their prices to customers and blaming the wholesale gas and electricity markets or the extra costs of environmental obligations," said Energywatch Chief Executive Allan Asher.

"The lid has to come off the wholesale gas and electricity markets and a good long look taken inside. Consumers may have to accept that prices will continue to rise. They should not accept this without good reason."

Shop around

Jennifer Evans, of price comparison service uSwitch.com, said power companies could "justify" the prices rises of the last 12 months.

The cost of wholesale gas has risen 28% since November 2003, wholesale electricity has jumped 20%, and firms were being forced to make infrastructure investments.

But she advised consumers to shop around.

"Unfortunately, the rises are understandable - but they do vary from supplier to supplier," she added.

Powergen's gas and electricity prices rose by an average of 5.6% in January and gas prices will go up by an average 3.1% from 6 September, said Miss Evans. And British Gas, which raised prices by an average of 5.9% in January, are also expected to announce a further increase within a few weeks.

Scottish Power, Npower, Scottish & Southern, Telecom Plus and Atlantic Electric & Gas have all also raised prices this year by between 3.6% and 15.2%.

"Suppliers are reliant on consumer inertia," she said. "Despite rising costs, customers who've never switched before and remain with their incumbent supplier are paying over 20% more for their energy than necessary.