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
A 65-year-old man was attacked by a shark in Australia on Friday, leaving him with serious leg injuries.
Nearly one million people could have their homes repossessed because they do not have a plan to pay off their interest-only mortgages.
Social services officials think that Charlie Clift, five, and Kaiton Warnes, two, are in North Cyprus with their mother Amelia Warnes, 23.