Energy regulator Ofgem has proposed that the Big Six energy firms should be investigated by the Competition and Markets Authority.
In an open letter to Britain's main energy suppliers, the regulator's chief executive officer Dermot Nolan said they were concerned that companies were "not passing on savings to customers".
He said: "A concern that savings were not being passed on to customers was one of the reasons why we have proposed a referral of the energy market to the Competition and Markets Authority for investigation."
More top news
An American serviceman has been killed "as a result of enemy fire" in Iraq, officials have confirmed.
The parents of five-month-old Nora Hall are preparing to turn off their daughter's life support machine after she suffered a massive stroke.
Following some interesting conversations with key Labour personnel, here's where I think the party is right now.