The survey has sparked calls for government to intervene and prevent price comparison sites and suppliers from “exploiting loyal customers”.
Fifteen per cent of customers were found to have stayed with the same supplier for five to 10 years, and paid a total of £5.85 billion extra. Meanwhile the 7 per cent who had not switched for 10 to 15 years had collectively overspent around £4.75 billion, and a further 10 per cent had stayed with the same supplier for more than 15 years, and overspent £8.1 billion in total.
The research, from energy comparison site Energy Helpline, considered how much customers had paid for their energy since deregulation if they hadn’t switched or had remained on standard variable tariffs.
Comparison site thebigdeal.com has blamed other similar sites: “Millions of non-switching Britons live at the mercy of their energy supplier. Few suspect their loyalty is taxed at £300 a year.
“What is even more depressing is that price comparison sites are helping the big six to exploit loyal customers. The big six sneak their best deals on to comparison sites as ‘exclusives’ while the sites refuse to allow existing loyal customers to take them. This practice is a disgrace and government must intervene to stop it.”
The research found that the main reason for staying with a supplier was quality of service (53 per cent).
Energy Helpline co-founder Mark Todd said: “The media talks a lot about broken trust between energy suppliers and customers but in reality there appears to be too much trust.
“If households continue to stay loyal, providers have no incentive to offer cheaper deals. The price of loyalty is truly vast. As energy companies are allowed to charge whatever they like in the UK, it’s important for customers to monitor their bills and not be scared to switch.”
The figures follow an investigation by the Competition and Markets Authority (CMA) which recommended a removal of the requirement on price comparison websites to show the whole of the market and only show tariffs from commission paying suppliers. The CMA argued that this would encourage comparison sites to offer exclusive deals.