I'm as qualified as any to have an opinion on the subject, I own two VW cars, both purchased brand new, one's a diesel touran and the other is an Up.
They both do their jobs perfectly, they were purchased to provide dependable, safe transport cost effectively, I'll keep them 'till they don't and therefore consider that I've already lost all the purchase price. When I want fuel economy I press the throttle less and avoid braking, but normally, I drive as fast as the law allows.
VW sold me exactly what I asked for, whether it's in the right tax bracket or not would make no difference to emissions, I'd be driving it exactly the same, the government would just have a few more pounds to spend on more studies or whatever they do.
The up will no longer be providing safe reliable transport however, some dozy bint in an SUV rear-ended it while stationary on Saturday and punted it 20ft across a yellow box junction. And here's the thing, why are we out to bankrupt one of the few companies who make good cars, lots of money was spent developing that UP to make sure a little farty car would be safe, four people were in there, the rear passengers only 12" from the front bumper of the dimwit, the boot floor is crushed but the passengers were completely unharmed.
I'm now in the market for a new UP and as far as I can see, they're not any cheaper!