How to assess how environmentally (un)friendly a vehicle is

From this autumn, anyone buying a new car in the UK will be able to assess how environmentally (un)friendly a vehicle is through a new system of colour-coded labels announced by the Department for Transport today. You'll have seen the same sort of scheme used in refrigerators and other white goods, although in my local showroom almost everything seems to have an "A" on the front, which I'm not sure is testament to widespread good design or poor standard-setting.
I think the new vehicle scheme will have a major impact on automotive design, especially if the UK is only one of many countries adopting something similar. The public understands simple coding systems like this. But it's important it's marketed well, and that the lowest "F" grade doesn't simply become associated with stupidly-oversized cars, and therefore become a "badge of honour" for certain sections of the population. Whilst a lot of customers will take notice of the coding (which also details how much motorists can expect to pay in fuel bills in a typical year), for others, the DfT will have to make it "cool" to have an "A"-rated vehicle.
If the government really wants to tackle the environmental problems caused by road vehicles, however, it needs to look more closely at supporting manufacturing-related initiatives. Making a car causes more environmental impact than running one does.