British Gas saw profits rise by nearly a third in 2015 as a result of customers using more energy, it said.
The energy company posted profits of £574 million, up from £439m in 2014. But profits at its parent company, Centrica, fell by 12% to £1.46 billion.
Last week, British Gas became the last of the 'big six' energy firms to announce a reduction in gas prices, following falls in wholesale prices.
In a statement, Centrica chief executive Iain Conn described British Gas' performance in 2015 as "resilient".
He added: "We have a clear strategy for delivering growth and returns built around the customer and I am encouraged by the progress we have made.We remain confident that our plans and underlying performance momentum will allow us to more than balance cash flows."
Along with its rivals, British Gas has the subject of a review by the Competition and Markets Authority (CMA) since last summer. The competition regulator believes consumers collectively overpaid on their energy bills by £1.2bn between 2009 and 2013.