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Energy giant E.On has said its standard tariff prices will rise by an average of 4.8% for those customers who take both gas and electricity.

Customers will face an average annual price rise of £55 from 16 August.

"A number of costs have risen quite sharply and we've experienced a hike in the price we have to pay for the energy our customers need," E.On said.

In March, the company made changes to its bills which added £22 to its average standard variable tariff rate.

An E.On spokeswoman told the BBC: "Those changes led to the removal of discounts and a change to the standing charge for people who pay on demand by cash or cheque.

"This is an increase in unit price, which makes us the fourth cheapest of the big six suppliers."

For E.On's electricity-only customers the standard variable rate will rise by 6.2%, an average of £36 a year, while gas-only customers will see a 3.3% increase, an average of £19.

She added that the company had been hit by a 22% increase in wholesale costs since March.

The rest of the big six have all announced prices rises recently.

SSE bills rose an average 6.78% or £76 a year

British Gas bills went up by 5.5% or £60

Scottish Power's increase was 5.5% or £63 on average

EDF raised electricity prices by 2.7% or £16

Npower's 5.3% increase, an average of £64, came into effect at the weekend.

In a statement, E.On said it was its second unit price increase in more than four-and-a-half years, and during this period it had also cut prices on two occasions.

E.On chief executive Michael Lewis said: "We'll continue proactively to tell customers about the different tariffs on offer and encourage them to move to those tariffs, as well as promoting the different services that can potentially help bring their bills down such as a smart meter, a more efficient boiler or better insulation."

Victoria Arrington, from price comparison service Energyhelpline, said: "This new rise is a bitter and expensive pill to swallow. The cost of sticking to a big-name energy supplier is quickly outstripping the feeling of safety it gives customers."