Elderly people across the UK could be getting overcharged by paying their energy bills by prepayment meter, cash or cheque.
Age Concern claims that those paying by the above methods are being overcharged a total of £1.3 billion a year
It added that the most vulnerable people, including the older generation, are the most likely to be using cash or cheque payments at a Post Office counter or bank as it makes budgeting easier.
The charity also claims that two-thirds of older people are concerned about their ability to stay warm and pay their energy bills this winter.
Gordon Lishman, director general of Age Concern, described the situation as "outrageous".
"Pensioners are clearly more worried about staying warm and well this year. Yet the impact of increased energy bills is causing thousands to risk their health by cutting back on heating," he added.
A source close to one of the leading six energy suppliers in the UK recently told the Times that future price cuts could be "modest", less than ten per cent, adding that many families are "likely to be disappointed".
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