Carbon footprint or physical footprint?
Why?
My engine is smaller and I make less trips than the 2.2L
Good points, I was referring to the size and not carbon footprint.
Why - Your MPV is for private use. As an exaggerated example if your MPV carried 15 people would you expect to pay even less road tax? You are a private individual, it was your choice to have a large family, it just doesn't make sense to offer you lower road tax based on the number of children you have. When your kids grow up there will be 5 more cars on the road as opposed to 2 or 3 for the normal family so in the long term it could be argued that as a result of having above average children you are creating more waste and pollution.
Your activities at home are a leading contributor to pollution :Smileysex