Energy suppliers have over charged a suspected 10,000 UK gas customers in a measurement mix-up.
E.on raised the issue when it realised meter readings were being confused with older imperial meters and modern metric ones.
This has now prompted other energy companies to check whether or not they have experienced the same problem.
The results of this problem meant that some people have been undercharged by about 60 percent while others were over charged by as much as 130 percent.
The revelation comes only a few days after Ofgem promised “to deliver a more competitive, fairer energy market for all consumers” in an aim to help consumers save money.
Energy UK, an industry trade body, is working with Ofgem to identify all customers affected by suppliers.
They said an “extremely small” number of customer accounts, 0.3 percent of households, had been affected and suppliers were working hard to rectify the problem.
E.on released a statement apologising for the mix-up: “E.on UK has said sorry and confirmed that around 350 residential and small and medium-sized enterprise customers will be refunded and appropriately compensated after the discovery of a potentially industry wide meter set-up issue.”
Ofgem said E.on has done the right thing in coming forward, and urged other suppliers to follow the rules it has put in place:
Ofgem said it has asked all suppliers to investigate if their customers have been affected and urged them to provide their results by August 19.