The unusually cold weather this winter helped drive an increase in revenue at Centrica, the energy company which owns British Gas, which hailed a 'robust' financial performance in the six months to June 30th.Group revenue from continuing operations was up 14% at £13.7bn after customers used more gas to stay warm during the prolonger cold snap. Average residential gas consumption was up 13% year-on-year and well above normal levels for that time of year.However, adjusted earnings rose by just 2.0% to £767m as bottom-line growth was held back by an increase in the tax rate as well as higher environmental and commodity costs at British Gas Residential. "With our customers using more gas to stay warm during the unusually cold winter, we're doing everything we can to help them keep their energy costs under control and make bills simpler and clearer," said Chief Executive Sam Laidlaw."We are also delivering for our shareholders, enabling us to continue to grow the business and invest to secure energy supplies for the future."Centrica raised its interim dividend by 6.0% to 4.92p per share.The firm said that, subject to weather conditions, commodity prices and asset performance, it remains on track to deliver earnings growth in line with expectations for the full year.The stock was up 1.35% at 391p by 09:57 on Wednesday.BC