The company, which checks an average of 500 bills a day on behalf of its UK client base, believe that the complexity of tariff structures has meant that energy suppliers are more likely to make mistakes and customers less likely to spot them.

According to the company, nearly 50% of new clients have been identified as overcharged, some for several years and while M&C Energy Group analysts continue to check clients' bills, it is more likely that new customers will get the biggest refunds.

Last year, M&C Energy Group were successful in returning £2m to their overcharged clients from the energy companies.

M&C Energy Group's Electricity Analyst, David Hunter explains: "Just because a bill adds up doesn't make it right. The vast majority of mistakes cannot be identified easily, which is why for our industrial and commercial customers, we run over forty different checks for potential areas of overcharging.

"The errors range from faulty meter readings or problems with supplier switching, to incorrect applications of tariffs or wrong assumptions on network charges.

"At a time when energy bills are at an all time high and energy companies continue to pull in big profits, it is a nice bonus for businesses to get their money back. We would urge all companies to check their bills."