Energy companies face "muscular and strong" action from the Government over prices after a "flagrant mistreatment" of customers, a minister has warned.
Business and Energy Secretary Greg Clark told MPs he planned to take "decisive action", although no date was given for any crackdown.
Addressing the Business, Energy and Industrial Strategy Committee, he said a two-year investigation by the Competition and Markets Authority had identified consumer detriment averaging £1.2 billion a year.
"We are not going to simply note the findings. I think there is an overwhelming appetite to sort this problem out once and for all."
Mr Clark said he was disappointed with the response from the energy companies, which have come under attack for raising prices.
"If the competitors in this industry don't see this as behaviour that is damaging consumers, I do - and I will act. The response will be muscular and strong and will apply to all of the companies who are disadvantaging consumers."
Mr Clark said the poorest households spent the most on energy but were least likely to switch to another supplier.
"I don't think it is acceptable that they should be exploited in that way."
Committee chairman Iain Wright asked the minister why he had not acted already, referring to a price increase announced last week by EDF.
Mr Clark maintained there was no delay, although he conceded that the market was not working.