RAC spokesman Simon Williams said: "Motorists and businesses will be aghast to hear the Transport Secretary hint at higher taxation levels for diesel vehicles. The present tax system has for many years favoured diesel over petrol vehicles, not least because diesel cars generally emit lower levels of CO2. Many drivers and businesses have, in good faith, invested in diesel cars for this reason. What is more, diesel drivers contributed almost £17bn in fuel duty last year and already pay some of the highest diesel prices in Europe.
"There is no doubt that action is needed to improve air quality, however by the Government's own admission this needs to be tackled at a local level. This is something clean air zones, proposed for a number of UK cities, can help address. Additionally, incentivising motorists to take up cleaner vehicles additionally is important.
"But there must also be a concerted effort to clean up older, more polluting bus and taxi fleets in towns and cities. The Government can also not ignore the fact that congestion levels can exacerbate pollution levels and must consider measures that keep traffic moving."