Customers of the Big Six energy suppliers are paying up to £234 a year too much in gas and electricity bills, a competition probe has found.
The Competition and Markets Authority (CMA) said 95% of dual fuel customers could have saved by switching tariff or supplier.
It said the average saving available to these customers was between £158 and £234 a year depending on the supplier.
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The findings were the latest update from the CMA's full-scale probe into the sector which is dominated by the Big Six firms - Centrica, SSE, npower, EDF, Scottish Power and E.ON.
It has updated a statement it published at an earlier stage of the investigation in July last year. The CMA said it had not yet reached any conclusions. Provisional findings will be published in May.
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