Energy suppliers have been accused of using underhand methods to charge customers more than they ought to.
According to industry watchdog Consumer Focus, many energy suppliers are not making their bills clear enough and this obfuscation allows them to overcharge consumers.
Methods used to overcharge consumers were found to include increasing the cost of best-buy deals a few months after customers switch energy tariffs, not informing customers of price hikes for up to three months and making false claims about the link between wholesale and retail prices.
According to industry experts, most households have no idea which tariff they are on or how their bills are calculated.
Adam Scorer, of watchdog Consumer Focus, said: "We are disappointed at how some suppliers are implementing Ofgem's changes and we want to see clear English on energy bills for customers. Bills have been confusing and a major source of frustration for too long."
Ofgem has introduced new regulations that force energy suppliers to give households an annual statement detailing much energy they have consumed within the last 12 months.
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