Tests used by automakers to find out how fuel efficient a model is do not provide the most accurate information to buyers, it has been claimed.
New tests from Channel 4’s motoring website 4Car revealed that fuel economy tests on eight low emission cars did not meet official figures.
It tested the Golf Bluemotion, Skoda Fabia Greenline, Mini Cooper D, Honda Civic Hybrid, Toyota Aygo, Ford Focus Econetic, Fiat 500 1.2, and the BMW 118d.
All these models are regarded as low emission vehicles and the real-life tests found that three cars were as much as 10mpg short of the published fuel consumption rate.
Further testing revealed that carbon dioxide emissions figures are unrealistic and claimed that all the cars should actually fall into Road Tax Band C.
Tim Bowdler, editor of 4Car, said that the official testing scheme was "too simplistic".
He said it did not "embrace all the vagaries of real-world operating conditions".
"It allows certain types of car to look good – too good," he added.
The Golf Bluemotion ran on 57.5mpg with 130g/km emissions, the Skoda Fabia Greenline ran on 60mpg with 124g/km and the Mini Cooper D ran on 61mpg and 123g/km.