Parent company Centrica said British Gas Energy has seen a 44 per cent jump in adjusted operating profit, which reached £118 million in 2021.
The business said it was helped by households using more gas in the first six months of the year due to unusually cold weather.
The unseasonably mild weather in the final three months of the year also allowed it to sell gas and electricity it had bought in advance, cashing in on high energy costs.
Centrica also said it plans to pay back the £27m that it claimed from the UK government to furlough its staff.
Chief executive Chris O’Shea has also agreed to waive his £1.1m bonus. His regular salary is £775,000.
His decision came as gas and electricity prices are set to increase on April 1 by more than 50 per cent for millions of households.
Across the group, Centrica posted a 20 per cent rise in revenue to £14.7 billion. Adjusted operating profit more than doubled to £948m.
Chairman Scott Wheway said: “In 2021, I’m proud of the way Chris O’Shea has led Centrica to deliver significant benefits for our customers and wider stakeholders.
“We have rescued more than 700,000 customers from bankrupt suppliers; our engineers have bravely stayed out on the front line, despite the challenges of Covid, to fix the heating of millions of homes; and we’ve done more than ever before to help support vulnerable customers to cope with the energy price crisis.
“Our financial progress and these achievements triggered an annual bonus entitlement for the CEO and it’s a mark of Chris’s exemplary leadership that, mindful of the difficulties many households face in light of the extreme rise in global energy costs, he has indicated to the board his intention to forfeit this entitlement.”
Andy Prendegast, national secretary of the GMB union, said: “It's good to see Centrica back in profit. But GMB won’t forget this comes off the back of a demoralised workforce working longer and harder to deliver them.”