The news service said that Britain's biggest gas supplier, British Gas, is expected to confirm on Thursday that about 370,000 customer accounts defected to rivals during the final quarter of its financial year. (http://link.reuters.com/wej96v)

The gas major is scheduled to release its full-year earnings report on February 20. The company could not be reached outside of normal business hours.

The group is expected to say on Thursday that its operating profit, which is forecast to be about 2.7 billion pounds, gives the company the scale to secure long-term gas supplies for the UK, Sky News said.

The "Big Six", (>> Centrica PLC) British Gas, SSE (>> SSE PLC), EDF (>> EDF), RWE npower (>> RWE AG), E.ON (>> E.ON SE) and Scottish Power (>> Iberdrola SA), which are the top suppliers of Britain's energy retail market have come under scrutiny for making profits by overcharging customers.

Sky reported that Centrica is expected to publish new data on Thursday aimed at supporting its argument that its profit margins on domestic energy supply are not excessive.

Soaring energy costs have also become a big political issue in Britain since opposition Labour leader Ed Miliband said in September he would freeze consumers' bills for 20 months if he wins the next national election in 2015.

Energy Secretary Ed Davey last week said former gas monopoly British Gas might be broken up to put a stop to excessive profit margins charged by Britain's biggest gas supplier.

British government started an annual energy market competition probe last year to address consumer complaints over increasing energy bills, the first report details of which are due end of March.

(Reporting by Aashika Jain in Bangalore; Editing by Bernard Orr)

Stocks treated in this article : EDF, Iberdrola SA, RWE AG, E.ON SE, SSE PLC, Centrica PLC