Re: Only 10%?
"The intention is that it's used purely as a relative comparator, not an absolute, so that you know that a car with an official consumption figure of 70 mpg will be more efficient than one with a 60 mpg figure, and not that either will actually deliver the quoted consumption figure"
That would work if they all cheated in the same ways, but it seems they don't, judging by the differences between real world figures found on the 'net and the official ones - some cars with some drivers are pretty close to official figures, others way off.
It would help if cheating was made more difficult - measure a vehicle's emissions whilst it achieves its stated 0-62 time for example.