Drivers and homeowners are being charged "exorbitant fees" for minor policy alterations and renewals, according to an investigation by Which? magazine.
Charges include up to £30 for minor amendments including change of address, updating personal details or transferring to other vehicles, the research showed.
Cancelling policies or even simply renewing a policy can also attract charges, the consumer group found.
Which? has criticised the charges for not being clear enough and not easily accessible to customers using an insurers website.
Research shows that both Axa and Swiftcover charge customers £30 to change their address, update their surname on marriage or change the vehicle covered by their motor insurance.
The same changes attract a £35 fee at Hastings, which also charges customers a £5 renewal fee.
50plus Insurance charges £10 for renewal, while both companies charge a flat £10 set-up fee.
Cancelling a policy also attracts fees, with Budget Insurance charging £75 per cancellation of a car insurance policy and Axa, Zurich, Sheila's Wheels and More Than charging £50 or more for the same service.
The report also highlights the high interest charges attached to a number of policies when customers elect to pay by instalments.
Budget Insurance, Axa and Swiftcover all charged between 29.3% and 32.3% interest depending on the policy. In contrast, Age UK and First Direct do not charge extra for their monthly payment options.
Which? chief executive, Peter Vicary-Smith, said: "It's a disgrace that insurers charge exorbitant fees to make basic changes to a policy. These charges should reflect the real cost to the company and not a way of making easy money from consumers who are already struggling with high and rising insurance premiums.
"We want insurance companies to be clearer about the fees that they charge and stop hiding the details away in pages of terms and conditions. The new regulator, the Financial Conduct Authority, must ensure that any charges reflect the actual cost incurred by the insurance provider."
The review of the terms and conditions found on the websites of 39 car insurers and 34 home insurers appears in the May edition of Which?
In response to the report, Swiftcover said: "When it comes to swiftcover.com and 'hidden charges', as Which? puts it, they have simply got it wrong.
"Swiftcover.com has always been an online-only insurer, allowing customers to change their policy online whenever they wish, and as often as they need to - without charge. If, however, a policyholder chooses to update their policy by speaking to the help desk, there is an admin charge of £30, like with many other insurers."
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