That's what he's basing it on though (CO2). It's unfair to tax people just because they want a type of car. I agree if we can make cars more efficient then great, but efficiency doesn't necessarily = CO2. My car does well over 210g/km of CO2, but I can achieve well over 35mpg if I drive sensibly and other more efficient cars produce maybe more CO2 and yet return more miles, so ecconomy is different to CO2 emissions. Heck there are some hybrid cars that have a huge 3.5L V6 but have some batteries, they still produce "high" levels CO2.
Yes the consumption of oil is high, but the accountability for cars is quite minimal in comparison to powerstations, manufacturing and other processes around the world.
CO2 and mpg are proportional.
The more fuel you burn the more CO2 you emit.