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.