Loyal customers of mobile phone and broadband operators, banks and insurers are being ripped off to the tune of £4bn a year – or as much as £877 per person – according to Citizens Advice, which has lodged a “super-complaint” with the competition watchdog.

The charity said customers who stayed with their utility providers were being unfairly overcharged and that measures must be taken to end “this systematic scam”.

Citizens Advice said its research across five sectors – mobile phones, broadband, home insurance, mortgages and savings – found British consumers were losing £4.1bn a year to the “loyalty penalty”: the difference between what existing and new customers pay for the same service. It added that eight in 10 people were paying a significantly higher price in at least one of these sectors for remaining with their supplier.

Using its legal powers, Citizens Advice has submitted its super-complaint – the fourth it has made since being given the right to do so in 2002 – to the Competition and Markets Authority (CMA), which must respond within 90 days.

A consumer who was overcharged across all five markets faced a potential total penalty of £877, made up of £439 for a mortgage, £264 for a mobile phone contract, £113 for broadband, £48 for a cash Isa account and £13 for home insurance.

Citizens Advice said the price cap for the energy market unveiled earlier this month would bring down loyal customers’ bills by about £75 a year on average but added: “Excessive prices for loyal customers can be just as high – if not more so – in other markets.”

Gillian Guy, the charity’s chief executive, said: “It beggars belief that companies in regulated markets can get away with routinely punishing their customers simply for being loyal. As a result of this super-complaint, the CMA should come up with concrete measures to end this.”

Possible outcomes of the complaint might include regulatory action such as new rules, changes to the law, a review or a referral of the matter to another body.

The £439 figure for mortgages is the difference between the amount a typical customer would pay after being moved from a two-year fixed-rate mortgage on to the lender’s standard variable rate, and the amount they would pay as a new customer taking out a fixed rate.

The charity has proposed that in the mortgage market, the “standard variable rate” label should be changed to the “expired rate” to better describe the nature of the contract.

In the mobile market, the loyalty penalty involves providers continuing to charge people the same amount after they have paid off the cost of the handset. The telecoms regulator, Ofcom, said earlier this week it was looking at ways of forcing mobile phone operators to stop the practice.

The £113 broadband figure is the difference between the cheapest basic deal and the price customers pay after the initial contract period ends, while the savings penalty relates to someone who took out a one-year fixed-rate cash Isa who is moved on to a poorer variable rate at the end of the period. The insurance figure is the average difference between the initial price a customer pays for buildings and contents cover, and the price offered on renewal after one year.

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The charity said it had also found the loyalty penalty was disproportionately paid by vulnerable consumers such as older people and those with mental health issues. These groups were particularly likely to struggle with switching.

In one example, Citizens Advice helped an older couple whose daughter discovered they were effectively paying nearly £1,000 a year too much on their home insurance. The couple, both in their 90s, had been with the same company for six years, and over that time their premium had continually risen.

Citizens Advice’s super-complaint on payment protection insurance (PPI) in 2005 led to changes that have contributed to £32bn being returned to customers in refunds and compensation to date.

A regulator is required to publicly respond to a super-complaint within 90 days to say whether or not it believes this is an issue, and how it intends to deal with the matter.