Customers of energy giant SSE have been urged to seek compensation from the company after Ofgem announced it is to be fined a record £10.5 million for "prolonged and extensive" mis-selling.
Chancellor George Osborne described the penalty - the largest ever imposed on a supplier - as "quite right" and said he would like to see the proceeds of future fines given to customers rather than the Government.
Energy watchdog Ofgem said it found "failures at every stage of the sales process" across SSE's telephone, in-store and doorstep selling activities, adding that the level of the fine reflected the seriousness and the duration of the mis-selling, as well as the harm caused to customers and the likely gain to the company.
SSE provided "misleading and unsubstantiated statements" to potential customers about prices and savings that could be made by switching to SSE, according to Ofgem.
Management at SSE - one of Britain's "big six" energy suppliers - failed to pay enough attention to compliance, which allowed the mis-selling to take place, added Ofgem.
Mr Osborne told ITV: "SSE have treated their customers badly and it's quite right they've got this big fine. But I'd like to see changes, first of all so that in future these fines can go back to the customers rather than to the Government, and second so that these energy companies are forced to put families on the lowest tariffs to make sure people get the maximum help with their energy bills."
Ofgem does not yet have powers to require companies to award consumer compensation, so the fine will be paid to the Treasury.
Adam Scorer, director of policy at Consumer Focus, said: "This is not a case of one bad apple or one rogue sales team. The problems at SSE affected the whole direct selling operation and represent a fundamental failure at one of our biggest energy companies. Other companies have also broken direct selling."
SSE said it was "deeply regretful that breaches occurred and apologises unreservedly to any customers who have been affected by sales activity which ran counter to the values and culture of the company".
It insisted its sales practices have been overhauled since Ofgem launched its investigation, but admitted that it did not move fast or far enough. Any customers who believe they have been mis-sold to by SSE should contact its dedicated line on 0845 0707 388.