VW fixing their emissions tests on huge numbers of cars will have an impact.
Really, it won't make any significant difference (especially as the vehicles will have to be recalled anyway). Don't get me wrong - it's bad. But older diesel cars and, especially, lorries are far, far more polluting.
I think Gordon Brown promoting diesel cars had an influence in the short term, just in the wrong direction.
You're right that diesel emissions are an important issue.
However, the environmental argument about diesel versus gasoline engines is a complex one. Diesel engines are more efficient and produce lower CO2 emissions. However, for good scientific reasons, it is harder to control other emissions from diesel engines and this is why, historically, lower emissions limits were set for diesel than petrol cars, and why lorry emissions went virtually unchecked. That has changed now. Current emissions limits for diesel and gasoline cars are close to identical.
Don't think you can blame the weather either.
Weather plays a huge role in dispersing pollutants. It's not a question of "blaming" weather; it is simply a fact that if you take a one-off measure of, say, ozone levels, one of the main factors influencing that measurement will be the prevailing weather conditions!
There are simply too many cars, and we have an economy that orbits around vehicle ownership and upkeep.
Not going to argue with you there ;)