It is likely that both petrol and diesel cars are likely to be taxed more heavily in the future, but the reality is that the vast majority of cars currently on the road still use fossil fuels and millions of motorists will not be able to afford an electric vehicle, so they will continue to use ICE vehicles for years to come. Diesel vehicles will likely attract higher tax in the future than petrol, but it is worth balancing this against the fuel economy of a petrol Touareg against a diesel model. The more miles you do each year the more sense the diesel will make over the petrol, so it is worth doing some basic calculations to work out what is best for your needs.