According to comparison site uSwitch.com, the average customer is overcharged by as much as £196 and often has to wait almost two months before they get their money back.

A staggering 95% of cases are identified by the customer rather than the bill provider.

The findings suggest that companies responsible for essential bills such as utilities, telecoms and mortgages, may have overcharged customers by as much as £6.7bn in the last 12 months.

uSwitch.com said that a third of consumers had been charged more than once for the same bill, with one in 10 having to pay three times in the same year.

While the average amount people have been overcharged is £196, more than one in ten have been overcharged by £400 or more.

Ann Robinson, director of consumer policy at uSwitch.com, said: “Overcharging on household bills is rife and yet it still seems to be down to the customer to spot it. Consumers have to keep their wits about them and ensure that they check all their household bills carefully – if you are not checking then the chances are that a mistake will have slipped through and this could be costing you dear.

“At the same time I would urge companies to do as much as possible to help their customers by making household bills simpler, clearer and easier to understand. This is a foundation stone in building trust and confidence, and a vital step towards putting consumers in control.

“With 95% of overcharging spotted by customers rather than the bill provider, it’s imperative that people are able to spot and resolve any mistakes quickly – nobody can afford to be left out of pocket because a company didn’t quite get its sums right.”

The most common causes of overcharging were: charges added that shouldn’t have been (42%), incorrect tariff or product details being used (32%) or a special offer or discount not being applied to the bill (25%).

A quarter of consumers also received bills that simply didn’t add up.

Those who were overcharged in the past year had to wait 53 days or almost two months on average to get their money back again. More than one in ten (13%) had to wait between two to six months. However, more than one in ten are still trying to get the issue resolved, while 6% never got their money back again.

The report also revealed that consumers were forced to spend an average of 8 hours and £23 on phone calls and correspondence trying to sort out overcharging.

Just 7% were automatically refunded these costs by the company involved.