Eco cars branded gimmicks as tests show they release up to one and a half times as much emissions as makers claim

Low emission "eco cars" release up to one and a half times as much carbon dioxide as their makers claim, according to road tests.

Three "environmentally friendly" models performed so poorly that they were branded gimmicks that cash in on growing concern about global warming.

A further five also failed to match their advertised emissions figure - including VW's Polo BlueMotion which was the first to go below 100grams of CO2 per kilometre.

The worst offender in the checks by Auto Express magazine was Honda's Civic Hybrid. It was found to emit 171g/km compared to the 109g/km claimed - 56 per cent more.

The magazine said the car's electric motor is "not strong enough to propel the oddball four-door Civic on its own" and it "failed to match the firm's economy claims".

The other "gimmick" cars were the luxury Lexus GS450h - the model leased by Tory leader David Cameron to show his green credentials - and Skoda's Fabia Greenline.

But the magazine was impressed by the technological innovations introduced to cut CO2 and said five of the cars could be considered 'green' despite failing to live up to claimed figures.

They are Ford's Focus ECOnetic, the Mini Cooper Clubman D, VW Polo BlueMotion, Seat Ibiza ECOmotive and Toyota Prius.

Auto Express says carbon emissions have become the yardstick by which a car's "greenness" is measured and can make or break a new model.

Editor David Johns said it was crucial that consumers know whether cars billed as eco-friendly are "truly green or really just pure gimmick".

The official figures are based on laboratory tests conducted by the manufacturers, importers or independent test engineers. They are a big selling point in adverts and affect the levels of road tax paid.

Honda denied the Civic Hybrid was a "gimmick" and insisted its carbon emissions were lower than other four-door saloons.

A spokesman said: "The quoted figures are generated from standard Government tests so that customers have a benchmark to compare one car with another.

"They are done in laboratory conditions and do not necessarily reflect driving conditions."