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Bentley, Porsche cars less reliable than inexpensive rivals, UK survey

Many would assume that the more expensive a product is, the more efficient it's likely to be. So you'd be right in thinking that a Porsche would be better than a Smart car, right? One survey may make you think twice about that.

British luxury automaker Bentley Motors has been named as the least reliable used car manufacturer of 2015 in the U.K., followed by Porsche, according to a recent survey.

What Car? and Warranty Direct on Thursday published their annual study, which analyzes and calculates 37 manufacturer brands—using a "Reliability Index"—to see which cars will keep passengers happy for the longest when it comes to functioning properly.

A strong trend that appeared in the survey was that affordability trumped luxury when it came to dependability, with luxury brands scoring lower on the list because of breakdowns.

Bentley

It wasn't helped by the average cost of repairs, which was higher for most luxury brands, compared to the typical household car.

Japanese brands seem to be popular among the Brits, with car manufacturers Honda, Suzuki and Toyota all taking the top spots as "most reliable" used car manufacturers.

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Honda came out on top for the ninth year in a row because of "low failure rates" and how affordable repairs are—for instance its cars cost less than half on average to fix at £335.87 ($501), compared to Porsche ($1,170) and Bentley ($1,012).

In terms of a particular car model, the most reliable were the Honda Jazz and Mitsubishi Lancer, which also doesn't break the bank when it comes to standard repair rates. Meanwhile, the Audi RS6 was considered the least reliable model overall, with an average repair charge of $1,495.

With a Honda Jazz ES Plus priced at £15,395 in the U.K. market, it's not surprising that the country's homeowners would opt for it when a Bentley Flying Spur V8 costs a whopping £156,145—more than 10 times the price of the Honda model.

Jim Holder, editor of What Car?, said in a statement that "Reliability is always one of the key attributes buyers look for when considering a used car purchase, so manufacturers that consistently demonstrate durability will always do well with the consumer."

In light of this survey, however, Porsche released a statement stating that it provided "just one snapshot of British consumer experience," adding that in bigger consumer markets, the results are different. For instance, the automaker told CNBC in an email that for the 10th year running, J.D. Power's APEAL survey ranked Porsche highest among new car buyers, in the U.S.

Bentley responded to the survey with a statement, sent to CNBC via email, saying that the survey was "not an accurate reflection of the Bentley ownership experience."

In terms of repairs, the company said that "the cost of owning and maintaining a Bentley is never going to be directly comparable with the other cars in this survey."

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When asked by CNBC about Bentley and Porsche's results, Holder said that as "the average cost of repair is factored in to the index, it puts luxury cars at a disadvantage compared to more normal brands with lower parts costs."

"The survey shows that if reliability and servicing costs are a priority then there are some brands that have a far stronger record than others, and that you would be well-advised to stick to them," Holder added.

The Reliability Index was published based on the calculations of each vehicle's "reliability," which looked into each car's failure rate, cost of repair, age and mileage. It used 50,000 live insurance policies from Warranty Direct, analyzing cars that were between 3 and 8 years old.