British Gas has reported a profit increase for the full year of 11% to £606m.
The company said it performed well in the 12 months until December 31, despite a weak economy and energy cost increases.
It said: "This is having a real impact for both residential and business customers and, against this backdrop, it is important that we continue to focus on improving customer service and reducing costs."
Overall, group adjusted operating profits rose 14% to £2.7bn, but Centrica, which employs around 40,000 people, said it paid more than £1bn in tax and invested £2.7bn in 2012.
Centrica said the sharp profit increase at British Gas residential came after last year's colder-than-normal weather saw gas use leap 12%, despite a fall in customer accounts.
The company said the number of residential customers dropped 1% in the year to 15.7 million, compared to 15.9 million in 2011.
It said customer "churn" was at its lowest rate ever.
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The results are likely to raise questions over the fairness of energy bill increases after British Gas raised tariffs by 6% for around 8.4 million households at the end of last year.
To help thwart criticism the company provided a breakdown of the average customer bill, which it said totalled £1,188 a year.
It said the average wholesale energy cost for a customer was £568, delivery to the home was £283, environmental and social policies £112 and tax of £72.
The company said its own operating costs were £104, leaving a profit of £49.
Chief executive Sam Laidlaw also addressed the issue of corporate tax responsibility, amid the public furore over multinational tax avoidance.
He said: "It's important that Centrica makes a fair and reasonable return so that we can continue to make our contribution to society and invest."
British Gas said the growth of online accounts was 20% last year, with 3.4 million customers using web access.
More than a third of all energy bills are now sent electronically. Some 70% of customers' meter readings are now sent online.
It also revealed that it has struggled to lure new customers to the maintenance arm, British Gas Services, and boiler installation services dropped by 10%.
It said: "The economic impact was seen more clearly in British Gas Business, leading to lower profitability and a reduction in the number of accounts served in a highly competitive market."
On Tuesday Sky's City Editor revealed that the company would announce its ambitions to become a big player in North America and the global energy sector.
He revealed that Mark Hanafin, the executive who runs Centrica Energy, the division focused on exploiting UK and Norwegian gas reserves, will head a new unit focused on broader international upstream effort.
Centrica also confirmed that British Gas' managing director Phil Bentley would leave the company this year.
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