Energy companies have been ordered to refund customers affected by a mistake in gas meter readings.
The industry’s regulator Ofgem said it had written to firms about the error which has affected several thousand customers.
The mistake is believed to have occurred when imperial meters were confused with metric ones, according to the Financial Times.
The older meters measure usage in cubic feet whereas newer ones use cubic metres.
An Ofgem spokesman said: “We have written to suppliers and asked them to refund affected customers.”
The error has affected about 0.04% of all 27 million customers in the UK, which amounts to more than 100,000.
Some customers are likely to have been undercharged if their metric meters were read as imperial, while others will have been overcharged if the reverse happened.