One of the "big six" energy companies is to offer its electricity for sale to any household supplier, it has been reported.
According to the Financial Times, Scottish and Southern Energy (SSE) will break ranks with rival utilities by auctioning its power on the open market.
The move comes after Labour leader Ed Miliband pledged during his party conference speech to break up the "rigged market" in energy which delivers massive profits to a few giant companies and swollen bills to consumers.
The big six companies currently sell most of the electricity they generate directly to consumers.
SSE plans to auction 100 per cent of its power on the UK's day-ahead wholesale market by early next year, and will buy all the electricity its customers need from the same source.
It will phase in auctioning from Friday, and aims to auction 25% of its power by the end of November, it was reported.
The move could remove one barrier to entry for new suppliers, which could drive down consumers' bills as a result of greater competition.
Ian Marchant, chief executive of SSE, told the newspaper he expected "one or two" of his competitors from the big six to follow suit by Christmas.
Mr Marchant said the move was "one feature" of his company's efforts to restore the trust of customers.