The body also pointed out that many poorer customers were unable to get some of the best deals for them owing to many companies offering the best deals online, when some consumers do not have internet access.
Allan Asher, the chief executive of energywatch, said: "Consumers without internet or banking facilities are excluded from better deals.
"These figures show that the welcome actions by some suppliers to combat fuel poverty are offset by the extra costs and poorer service inflicted on those forced onto prepayment charges."
energywatch also recently stated its disappointment that consumers were to be hit by price hikes on their energy bills due to Ofgem's new gas price controls.
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