Energy companies are commonly owed much more money by people who leave unpaid debts behind them than the surplus that is left in accounts, a spokesman for the industry's trade association Energy UK has said.
He said suppliers agreed with ministers last year they would take "all reasonable steps to trace customers who leave a credit balance behind" but often face stumbling blocks because of a lack of account details.
Although companies are working to return money where there are credit balances sometimes former domestic customers provide no new contact details so suppliers don't know how, or to whom, they can return the money.
The most common reasons energy companies end up holding funds are when the bill payer has moved home or when a customer dies and suppliers have no record of the next of kin.
More top news
Duncan Jones tweeted: "1 month since dad died today. Made this card for him at Christmas. Due in June. Circle of life. Love you, granddad."
More than 10 days after his body was found, Richard Cole's family claim they are still in the dark over the circumstances of his death.
A cold and frosty start, then staying largely dry with plenty of sunshine.