The energy watchdog estimated that the 'Big Six' are making around £400 million from the high charges.
Speaking on the behalf of the organisation, Graham Kerr said the research provided "hard evidence" of profits being taken from vulnerable customers at time when fuel poverty is rising.
He added: "Instead of taking from the rich to give to the poor, it seems that energy companies are taking from the poor to give to the rich."
energywatch was established in 2000 to protect and promote the interests of gas and electricity customers in the UK.
The body provides impartial advice to consumers and also takes up complaints for those who have had difficultly in having their problems resolved by energy suppliers.
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