Over 11 million households – 42% of all homes – could be owed £1.5bn from their energy providers, up from the £1.1bn estimated last year.

uSwitch data revealed that the average household in credit could be owed £132 and almost one in ten could reclaim more than £200.

The findings come as the UK had the third mildest winter since records began, meaning millions of consumers paying by Direct Debit used far less energy than they paid for.

Shockingly, despite the majority of households having built up credit over the winter, 13% of consumers – over 3.5 million – are in debt with their supplier.

uSwitch is urging customers to submit regular meter readings throughout the year, to ensure accurate bills and to avoid the risk of accumulating significant credit or debt.

Some suppliers automatically refund credit balances once a year, but this may be subject to a minimum amount and refund policies vary between providers.

However, under energy regulator Ofgem rules, customers are able to request a refund of credit, as long as up-to-date meter readings have been provided.

Tom Lyon, uSwitch energy expert, said: “After one of the UK’s mildest winters on record, millions of consumers may well have paid out hundreds of pounds for energy they simply didn’t use. Under Ofgem rules, providers must repay any credit on request, so now is the time to read your meter, update your account and reclaim what you’re owed.

“The findings underline why providing regular, up-to-date meter readings is so important – it’s the only way to make sure you only pay for what you use and avoid the risk of falling into significant credit or debt.”

Lyon added that for anyone who finds themselves in debt, they should speak to their supplier about managing the account to prevent the situation deteriorating further.