However, the body has added that it is yet to discover any evidence of price fixing by any of the UK's leading energy suppliers, but stated anyone with proof of such behaviour should come forward.
Alistair Buchanan, the regulator's chief executive, said that the probe will consider if the market is still working well for all consumers in the UK.
He added: "Customers certainly should not stop switching as there are still big savings to be made by changing your price plan, your supplier and the way you pay."
Scottish and Southern Energy is the only supplier of the 'Big Six' not to up its prices, but stated it is planning to review its tariffs at the start of British Summer Time.
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