Thousands of customers may have been overcharged by energy companies because of basic mistakes in gas meter readings.
Energy regulator Ofgem has written to energy suppliers about the error which is known to have affected about 0.04 per cent of all 27 million customers in the UK, which amounts to more than 100,000.
The error was blamed on companies confusing old imperial gas meters, which measure usage in cubic feet, with newer metric ones, which measure it in cubic metres.
Ofgem said that some customers might have undercharged if their metric meters were read as imperial.
An ofgem spokesperson said: “We have written to suppliers and asked them to refund affected customers.”