The two energy suppliers being probed by Ofgem for charging customers over the odds have been revealed.
EDF Energy and Scottish Power are the companies under scrutiny from the energy regulator amid serious concerns that customers are paying too much for their energy based on where they live or are being overcharged if they use pre-payment meters.
The energy suppliers were found to be giving higher bills to customers living in the company's core area, where they tend to have the most customers.
It is believed the companies have been charging less in their non-core regions, where they are trying to persuade customers on rival tariffs to switch energy suppliers.
"Ofgem has demanded explanations from two suppliers under the first stages of a process which can lead to enforcement action if it isn't satisfied with the response," the regulator said.
Ofgem explained that energy suppliers can charge more for certain tariffs if customers' bills cost more to process but only enough to cover those costs.
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