Gas firms 'stockpiling £490m'

The overpayments are caused by direct debits failing to drop as soon as suppliers lower their prices.

Gas companies take up to six months and in some cases a year to review their customers' monthly payments and direct debit customers are in credit to their gas companies by an average £56 each, according to moneysupermarket.com.

Powergen was named the firm with the most customer cash "on float" at an average £78 each for those paying by direct debit, said the price comparison website. Npower comes second at £67 followed by Scottish Power, which is also above the average at £58.

The website's findings were based on a survey of 2,407 British adults of which 88% had mains gas supply. The average amount by which the respondents were in credit to their gas suppliers was multiplied by the number of houses in Britain to reach the £490m total overspend.

Moneysupermarket.com head of utilities Paul Schofield said six months was an "unacceptable" period of time to overpay for gas.

"Six out of 10 customers pay by direct debit and gas suppliers are going to continue to stockpile customers' excess cash over the coming months," he said.

Duncan Sedgwick, chief executive of the Energy Retail Association, which represents all the major suppliers, said for every person in credit there was at least another in debit to their gas firm. Customers use triple the amount of gas during the winter compared to summer. Paying a fixed monthly amount spreads the cost evenly over a year, he said.

"All the energy suppliers regularly review the amount of their customers' direct debit payments and people can call their company at any time to discuss the amount they should be paying," Mr Sedgwick added.

"We are at a loss to understand how these figures have been calculated as our analysis finds that these figures simply do not stack up."