Insurers are hitting consumers who buy policies through price-comparison websites with higher premiums.

Some costs are almost 50% more than they would be going to the insurer directly, figures from consumer group Which? show.

It means thousands of people who believe they have the best deal are paying over the odds for home and car-insurance policies.

For example, a Bradford & Bingley home-contents insurance policy was quoted at £72 on Moneysupermarket, £83 on Confused and £100 on Gocompare, even though the same risk profile was used.

By going to the insurer direct, researchers were offered the same deal for £68 — 47% less than Gocompare.

Some Post Office and Budget insurance policies were also more expensive via price-comparison sites.

A Post Office car-insurance policy cost £321.47 via Confused, but was £307.67 when bought directly. Budget charged £76.45 direct for contents insurance — a figure that rose 22%, or £17, when researchers sought a quote via Gocompare and Moneysupermarket.

“Aggregator sites have their use, but consumers need to check different sites as they offer different deals,” said Cathy Neal at Which?

“They should also check with an insurer direct to make sure they are getting the best price.”

A recent audit of quotes given to consumers by Confused found that 4% of quotes were cheaper if users went to insurers directly — equating to about 40,000 quotes per month.

Moneysupermarket and Confused said that their contracts with product providers stipulated that they could not offer cheaper deals to customers going direct.

“We’re constantly monitoring quotes to make sure this doesn’t happen,” added a Confused spokesman.

Bradford & Bingley said it did not have such a deal with any of the aggregator sites it is listed on and conceded that prices offered to consumers varied.

“Not all comparison sites operate on the same basis and, while we may offer the same product through these sites, they each charge us differently,” said a spokeswoman. “It can sometimes be necessary for us to adjust our pricing to manage customer volumes.”

The Post Office said it is sometimes able to offer better deals to customers buying directly.

Comparison firms, which charge product providers commission, are increasingly influential.

Latest figures from Comscore, an analyst, show that 13.4m people used sites to compare financial products in July.

Moneysupermarket, the largest comparison site, last week announced interim pre-tax profits £14.4m — an increase of 113% on the previous six months.

Budget and Gocompare said they were investigating the findings of the Which? report.