If its environment related excuse, its stupid....because efficiency relates to the torque profiles you employ for the vehicle (be it a massive truck to a tiny moped).
The larger the engine (and assuming vehicle is designed ok to use the output), the better it is for efficiency (holding everything the same) if you have a high torque regime (either hauling a lot or doing lot of city style stop and go, stop and go etc).
It is why I got much better gas mileage on my chevy silverado compared to the ford ranger i had some time back.
The best environment policy is to restrict traffic in dense city centres to begin with and have good public transport....rather than cut based on engine size....I mean if its engine argument, it should be engine age + base engine efficiency than anything else....not raw size/output which is a very complex variable w.r.t pollution/efficiency.
For that analysis I will need to see a up to date financial release from Walton
....
its coming up to 3 years now?
@Ashes @Michael Corleone @BDforever