Nearly a third of UK households have stuck with their home insurance provider for more than five years - potentially paying more than they need to, Citizens Advice has found.
Around 31% have had their policy for more than five years - meaning they could be paying 70% more than a new customer would, it said.
For someone with the cheapest policy for buildings and contents insurance, this could be an extra £110 a year, on average.
Citizens Advice said companies can make large hikes in premiums when customers renew their existing policies rather than shopping around for a cheaper deal.
It said vulnerable consumers must be protected from the "loyalty penalty".
Older people are particularly likely to have stuck with their provider, the research found.
Some 40% of people aged over 65 have had their home insurance policy for more than five years.
Gillian Guy, chief executive of Citizens Advice, said: "Home insurance companies are taking advantage of people's loyalty, and it's older people who are suffering the most."
More than 4,000 people took part in the research.
Citizens Advice said some home insurance providers do not always fully comply with rules requiring firms to state the past year's premium at renewal.
James Bridge, head of conduct regulation at the Association of British Insurers (ABI), said: "Many customers benefit from shopping around to get the right policy for their needs at the best price, taking advantage of what are in effect introductory discounts.
"We recognise, however, that in a competitive market, those that don't shop around may not always get the best deal.
"This is why we pushed for the new rules on renewal notices displaying both the existing and new premium to prompt customers, including the over-65s, to think about shopping around.
"The FCA (Financial Conduct Authority) has identified that some firms have had implementation challenges with the new rules and we would expect them to work with the regulator to put them right."