The research, which was carried out by YouGov, also showed that one in eight of the nine million customers in credit are actually owed a sum of more than GBP100. The survey also revealed that a staggering 80% of those who are in credit with their gas supplier have never asked for their cash back.

The company attributed the unused credit to the fact that, after a winter of historically high gas prices for UK households, prices are dropping, but consumers are not adjusting their direct debit payments accordingly. Moneysupermarket.com warned that, as gas prices continue to fall, this stockpile will continue to grow, unless consumers take care over their payments.

The company’s research showed that 61% of UK customers currently pay their gas bills via direct debit, but warned that the majority of UK utilities review their prices on a six-month basis, while there are some that only carry out annual reviews.

Paul Schofield, head of utilities at Moneysupermarket.com, said: Households have been taking the strain of higher gas prices for far too long, and with an energy price war finally gathering pace, it is vital customers reap the rewards as soon as possible.

Moneysupermarket.com named and shamed the worst of the UK utilities, reporting that Powergen’s customers have the highest average amount of cash held on float (GBP78) and the highest percentage of customers in credit to over GBP100 (26% compared to 12% national average).