While Which? also said some home insurers were charging nearly 35 per cent APR on monthly payments.

Which? asked 39 car insurers and 34 home insurers what APRs were being applied to monthly payments.

Many insurers did not disclose their APR. Among those that did, Which? found that 1st Central charges between 5% and 39.11%. It gives customers a personal interest rate after a credit risk assessment, Which? said.

The average rate across 27 providers that charge interest and disclosed their rate was 23.37%.

Only two car insurers asked – NFU Mutual and Hiscox – said they do not charge interest on monthly repayments.

1st Central told Which?: “We understand it is important to customers that we keep the price of insurance as low as possible – and benchmarking tells us that we are competitive for both annual premiums and for those that wish to pay monthly through a credit arrangement.

“We offer a range of APRs from 5% to enable us to provide credit to as many customers wishing to pay monthly as possible, including those with low or poor credit scores. Over the past quarter less than 2% of customers paid our highest APR.”

For home insurance, the highest rate in the Which? study was from Co-op Insurance. Which? found that customers pay between 31.31% to 34.75% APR on monthly payments.

Co-op Insurance works with partners to provide insurance cover – and it said it is looking to reduce rates where possible. It added that it chose to share its rates with Which? as it is committed to transparency.

Fifteen home insurance providers surveyed said they do not charge interest: Bank of Scotland, Halifax, Hiscox, HSBC, Lloyds Bank, MBNA, M&S Bank, Nationwide Building Society, NFU Mutual, SAGIC, Sainsbury’s Bank, Santander, TSB, Urban Jungle and Yorkshire Building Society.

Which? said that, in January this year, the average credit card rate was 34.8% with the majority of cards charging up to 25%.

But Which? argued that the risk to insurers is lower than for credit card providers, because the credit being offered is directly linked to the sale of the insurance policy and non-payment by customers can lead to the cancellation of the policy.

Since January 2022, motor and home insurers have been required to provide fair value on their products and those requirements have been further strengthened by the introduction of the Financial Conduct Authority (FCA)’s Consumer Duty last year.

Which? said the regulator should produce an action plan to make sure that firms are providing fair value in the interest rates they are charging customers. It called for a league table of providers to be produced by the regulator.

Rocio Concha, Which? director of policy and advocacy, said the FCA should “step up and to get tough with firms”.

A spokesperson for the Association of British Insurers (ABI) said: “Our members understand how important access to appropriate insurance is for their customers and are very aware of the financial pressures households are currently under.

“Paying premiums by monthly instalments is an option they offer to help customers manage their budgets.

“The cost of premium finance is one of a number of topics we continue to discuss with our members and the Financial Conduct Authority.”

An FCA spokesperson said: “Premium finance helps people to spread the cost of insurance. We have made it clear to industry they need to ensure people are getting fair value from it.”