Operating profits at British Gas rose 24% in 2010 to £742m, its parent company Centrica has said.
The news comes two months after the UK utility announced a 7% rise in domestic energy bills, which it blamed on rising wholesale prices.
British Gas said it had increased its number of customers by 267,000 during the year to 16 million.
The results helped Centrica to achieve pre-tax profits of £2.8bn, with operating profits up 29% to £2.4bn.
The 24% rise in British Gas's operating profit was largely because of an increase in profit per customer, with the number of customers up just 1.7%, as revealed in the group results of its parent Centrica.
Some 85% of British Gas's profit came in the first half of last year, according to a Centrica spokesperson, when customers increased energy usage in response to cold weather, and the firm attracted new business with a price cut in February.
The second half was less profitable for the group's residential energy unit as wholesale prices rose more quickly.
Centrica has claimed the decision in November to increase British Gas customers' energy bills was necessitated by a 67% rise in wholesale gas prices during the year, and a 29% rise in the cost of wholesale electricity prices.
Price comparison website Moneysupermarket.com called the rise in British Gas's profits a "real bitter pill to swallow for Britain's hard-pressed households who have suffered the double whammy of an extremely cold winter coupled with high gas and electricity prices".
British Gas launched what the comparison website considered the cheapest online tariff on the market in February.
But Moneysupermarket's Scott Byrom said that "customers shouldn't be fooled" into thinking British Gas was the cheapest provider overall because its standard, and most popular tariff, was still much more expensive.
"British Gas is the only major UK energy supplier that breaks down its results in any great detail," notes Mike O'Connor, chief executive of Consumer Focus. "As such it acts as a lightning rod for the industry."
Amid allegations that energy suppliers were making excessive profits, government watchdog Ofgem announced a review of the retail energy market in November, that is expected to be published at the end of March.
"The issue is not about one company or one year's profit or loss but it is about whether the energy market is working properly and Ofgem's review must try to answer this question once and for all," said Mr O'Connor.
"There is a compelling case for much more transparency across the market."
Centrica comprises a lot more than just British Gas, including business energy supplies and power generation, as well as substantial operations in North America.
Indeed, its UK residential energy supply unit contributes just 37% of the energy group's revenues.
Operating profits at Centrica's upstream business - which deals with power generation and oil and gas drilling, among others - were up 46% to £771m.
The company has been expanding quickly, according to chief executive Sam Laidlaw, with two major acquisitions last year designed to secure new sources of gas, and to expand into nuclear energy.
"We invested £4bn," he said. "Clearly therefore we have a much bigger group [than just British Gas]. We've been investing £1.60 for every £1 of profit for the group."