British Gas will increase prices for 3.5 million customers from October, its parent company Centrica has announced.

The British Gas Standard Variable Tariff, which was withdrawn for all new customers on March 31, will increase for existing customers on Oct. 1 by 3.8 percent.

This takes the average bill for a typical dual fuel customer to 1,205 pounds (1,556 U.S. dollars), just below the average of the SVTs for the larger energy suppliers, and represents an increase of 44 pounds (57 dollars).

Centrica explained that the price change is due to the rapid increase in wholesale energy costs since early April, when they last announced an increase in the Standard Variable Tariff.

"We are increasing our prices because of an approximately 20 percent rise in the costs of buying wholesale energy since April, as Ofgem cited when they announced an increase in the level of the prepayment meter cap on 7 August," the company said in a statement.

Centrica said they will contact 3.5 million customers who are affected so they know how their prices will change and let them know about their alternative fixed-term offers, adding that 2.4 million customers on fixed price products will be unaffected by this price increase.

Mark Hodges, Chief Executive of Centrica Consumer, said: "We have today reluctantly announced plans for an increase in our Standard Variable Tariff (SVT). We understand that any price increase adds extra pressure on customers' household bills. However, this reflects the sharp rise in wholesale energy costs."

"Until now, we have been able to shield customer bills from the full impact of the increase in the wholesale costs because of the way we buy energy in advance," he added.