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."
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This morning the prime minister spelled out her belief that we can thrive outside the single market.
"Important clarity" or the grounds for the "theft of democracy"? The PM's declared aims for negotiations have received a mixed response.
A divided theme across the UK today