You grill the Government - Why penalise diesel cars?

Q: Will the Government continue to focus its pollution control on carbon dioxide? And will it continue to penalise diesel cars, even though they produce low CO2?
Nora Best, Leeds

SL: Our policies are aimed at reducing emissions of both greenhouse gases and air pollutants from road transport. The duty payable on petrol and diesel is the same, despite the higher energy content of diesel fuel.

Diesel cars pay a very small Vehicle Excise Duty supplement and a small company car tax supplement because of their higher emissions of air pollutants.