Energy suppliers withholding up to £1bn from customers

As many as ten million households are in credit with energy suppliers, entitling them to a refund for overpaid bills.

But with direct debits reviewed only every few months, firms are stockpiling "cash mountains" that earn them millions of pounds in interest.

The problem is worse this year because of price falls and lower consumption caused by warmer weather.

British Gas was also condemned by customers for introducing a billing system that overestimates costs.

Complaints tripled to 21,427 after it charged for far more energy than customers were using.

Complainants claimed they faced obstacles when they tried to get their money back.

Three of the four biggest foreignowned energy suppliers are fairer to customers in their home countries.

French- owned EDF Energy and Npower, owned by Germany's RWE, automatically repay customers in their home markets.

But customers here must do the legwork themselves. Internet comparison-and switching service Energyhelpline.com estimates they are in credit by an average of £100 a year.

Spokesman Mark Todd said: "Utility companies could be sitting on a cash mountain of up to £1billion by the end of the year.

"This is outrageous. This is money that is rightfully owed to customers."

British EDF customers must ask for their money if it is less than £150.

If they do not, EDF takes the money off their next direct debit.

According to the website Moneysupermarket.com, EDF's five million UK customers are each paying £46 in gas overpayments a year, boosting the firm's income by £230million.

At Npower, overpayments of more than £25 will be refunded to UK customers automatically, but they must demand smaller sums back.

Scottish Power, owned by Spain's Iberdrola, reviews direct debits every three months but customers must ask for overpayment refunds. Spanish customers do not overpay because meters are read every two months.

British Gas said customers with more than £80 in credit on their account will be offered a refund.