Centrica, the owner of British Gas, has warned that gas prices are set to increase again with price rises expected at the end of the summer.

Centrica has warned that wholesale gas prices for this winter are around 15% higher than last year. Last summer British Gas increased gas prices by 18% and electricity prices by 16% pushing up the average dual fuel bill to around £1,288 a year.

The energy supplier said it wasn’t just wholesale gas prices which had increased. Other costs have also gone up including transportation and environment subsidies imposed by the government.

Initially Centrica thought prices would increase by around £50 a year but this didn’t include the higher wholesale gas prices so that figure will undoubtedly go up. Higher wholesale gas prices are also likely to affect business gas prices meaning it’s as important as ever to compare business energy prices when your energy contract is due for renewal.

Centrica said “The trend for retail energy costs therefore remains upwards”.

Experts have warned that the 2011 Japanese earthquake is still affecting wholesale gas prices with a possible 28% increase in wholesale prices. Japan has just shut down its last working nuclear power station as reported by Utility Exchange and liquefied natural gas is still being shipped to the country to supply its gas fired power stations. These supplies would normally be delivered to Europe and the UK.

Household gas bills were down this year as a result of a mild winter and increases in energy saving by consumers.

Centrica said its own trading for the past year has been in line with expectations with higher wholesale gas prices and power prices helping its “upstream” operations.