The auto industry has hit back at a leading car magazine that says the latest eco-friendly models fall far short of the claims the manufacturers make for them.

The spat calls into question the validity of the industry standard vehicle tests used by manufacturers to test emissions.

“Eco-friendly or merely green gimmicks?” asks Auto Express in a review of eight cars which boast low emissions and miserly fuel consumption. The review says that some car makers are using green wash to bamboozle environmentally concerned buyers.

All eight cars tested show a significant difference between the manufacturers’ claims for carbon dioxide emissions and fuel consumption – arguably the two key measures of a car’s green credentials.

This is to be expected, says the Society for Motor Manufacturers and Traders (SMMT) because the tests used by manufacturers “don’t reflect real-world conditions”.

“[Manufacturers’] CO2 claims are based on simulated tests mandated by law,” a spokesperson for the SMMT told BusinessGreen.com. “Any tests done by third parties will differ from the [Vehicle Certification Agency] tests which are done on a rolling road. Real-world conditions are affected by so many factors, such as driving style, road conditions and tyre pressure.”

The Vehicle Certification Agency (VCA) is the government body charged with ensuring that vehicles used on UK roads comply with European and United Nations regulations. The Agency’s Whole Vehicle Type Approval Process (WVTAP), which all vehicles have to undergo, includes measurement of 48 vehicle parameters – including CO2 emissions and fuel consumption – carried out on a production sample at a manufacturer’s site approved and witnessed by a VCA officer.

The Honda Civic Hybrid IMA ES fares particularly badly in Auto Express’ review.

“[The] gutless electric motor hampers the saloon,” says the review. “The problem is, the electric motor gives only 15Kw, compared to 50Kw in the Prius and 147Kw in the Lexus. As a result, it’s not strong enough to propel the oddball four-door Civic on its own, so the engine is employed more than you’d expect… The IMA failed to match the firm’s economy claims in our test, too.”

Honda claims the vehicle emits carbon dioxide at 109g/km, whereas Auto Express measured its output 57 per cent higher at 171g/km. In terms of fuel consumption, Honda claims the vehicle runs at 61.4mpg, whereas Auto Express measured it 37 per cent lower at 38.2mpg. But Honda stands by its figures.

“We refer back to the industry standard testing,” a Honda environmental spokesperson told BusinessGreen.com. “We don’t know what the driving conditions were used by Auto Express.”

The VCA keeps a database of all its test results. For example, the WVTAP outcomes for the Civic Hybrid can be seen here, clearly showing the CO2 emissions and fuel consumption figures used by Honda. The VCA also vets manufacturers’ advertising to ensure car data is presented accurately.

The eight cars tested by Auto Express are: Ford Focus 1.6TDCi Econectic; Skoda Fabia Greenline 1.4TDi; Mini Cooper Clubman D; VW Polo Bluemotion; Seat Ibiza Ecomotive, Toyota Prius T Spirit; Lexus 450h 3.5 V6 SE; and Honda Civic Hybrid IMA ES.

The Civic wasn’t the only one of the eight given a drubbing by Auto Express. In the verdict “green or gimmick”, the Skoda and the Lexus – the latter as driven by Conservative leader David Cameron – also got a “gimmick” tag along with the Honda.

The fact that cars are found to be less green in real life than in VCA tests does not negate the efforts car makers have made in reducing CO2 emissions and fuel consumption, “which has reduced emissions from the auto industry as a whole”, says the SMMT.

“We encourage buyers to analyse the data and decide which type of vehicle and driving style will reduce their carbon footprint,” a spokesperson told BusinessGreen.com.