Britain's least reliable cars revealed

The UK's least reliable cars are prestigious, according to Warranty Direct's Reliability Index that covers vehicles up to eleven years old. But how has this been calculated? Warranty Direct has thousands of insurance policies enabling them to place information relating to failure claims into a database. This includes how frequently each model breaks, the cost of repairs, times off-road, and ages/mileages. As such, each model earns a Reliability Index Score. The lower the number, the better. The average score is one-hundred, but the best performers score less than twenty. The worst performers score 'several' hundred. Oh dear.

Let us consider a few examples. The Mercedes-Benz SL has a Reliability Index Score of 376. That makes this convertible the 'least' impressive in Warranty Direct's database. Oh dear, again. An SL - on average - is 5.52 years old with a mileage of 38,430 at the point of a claim - and the average repair costs £776.07 and takes an SL off-road for 2.90 hours. Curiously, the Mercedes-Benz CL, S-Class, and V-Class appear in the bottom ten of the Index too. These score 352, 274 and 248 respectively - and tend to be about six years old.

The Land Rover Range Rover makes an appearance in the bottom ten too, with a Reliability Index Score of 308. Sadly for its prestigious manufacturer, it is joined by the smaller Freelander with an unremarkable score of 230. These vehicles are – on average - 7.1 and 6.24 years old at the point of their warranty claims. Warranty Direct's bottom ten also includes the Renault Espace, Jeep Grand Cherokee, and - surprisingly - the Nissan Pathfinder and BMW 7 Series. These score 257, 250, 245 and 229 respectively. Tut tut tut.

But that only tells part of the story. Why? Because many of the cars in Warranty Direct's database are far from new – and manufacturers consistently work to improve vehicle longevity and to climb reliability surveys. This is evident, for example, from the JD Power Survey 2012. This evaluated factors including reliability relating to newer cars (January 2009 to December 2010). Here, Mercedes-Benz was crowned the fifth best manufacturer from twenty-seven, and Land Rover came twelfth. All despite struggling at Warranty Direct.

Right, general points. Whereas reliability has improved over the years, longevity is still heavily influenced by motorists. Drive aggressively and skip maintenance and you are asking for trouble. Luck plays its part too. Some new cars fall apart when they should be at their best, whereas some old bangers plough on. So yes, consider reliability surveys next time you buy - but take an overview from numerous sources. Then cross your fingers.

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