LONDON Britain's energy regulator told the country's main energy suppliers on Friday to do more to return over 400 million pounds ($670 million) owed to former customers which is sitting unused in closed accounts.
Ofgem said Britain's biggest six energy suppliers - Centrica-owned British Gas, SSE, EDF Energy, RWE npower, E.ON and Scottish Power - were holding money paid in credit by customers who then switched suppliers or moved house.
The regulator said the companies were not doing enough to ensure the money was returned to consumers.
"When many people are struggling to make ends meet, it is vital that energy companies do the right thing and do all they can to return this money and restore customer trust," Andrew Wright, interim chief executive of Ofgem, said in a statement.
The energy suppliers hold at least 202 million pounds from closed accounts of former domestic customers and 204 million pounds from former non-domestic customers, the regulator said.
Energy companies have been in the spotlight recently, facing backlash from the public and politicians over price rises.
The affordability of heating British homes shot to the top of the political agenda last autumn after opposition Labour leader Ed Miliband promised to freeze energy bills for 20 months if he won power in a 2015 election.
Ofgem said it was not possible to repay customers, suppliers should find ways to use the money to benefit consumers more widely.
The chief executive of the industry's representative body, Energy UK, said more often than not, energy suppliers were owed a lot more money than they owe to the customer.
"Energy companies try and make sure individual customers' money gets back to its rightful owners. However, more commonly energy companies are owed many times more money by people who leave unpaid debts behind them," Angela Knight said in a statement.
She said suppliers stood ready to repay the money where customers provided the necessary details.
($1=0.5974 British pounds)
(Reporting by Julia Fioretti, Editing by Belinda Goldsmith)