Mr Buchanan said the recent economic turmoil had put pressure on many households and the only way they could save money on their electricity and gas bills was by looking for a better deal online.
However, he claimed: "In a strong competitive market, we would expect prices to respond to such falls."
He added that there has been widespread "public dissatisfaction" with suppliers' recent response to the fall in wholesale energy prices.
"I believe you owe it to consumers, ahead of the winter, to explain how cost changes, including falling wholesale costs, are likely to bear on future energy bills," he concluded.
Last week, Ofgem proposed increasing the period in which customers can switch energy supplier following price changes.
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