While I am in agreement with the efforts to reduce CO₂ emissions, Thomas Glanville (December 5) gets it wrong when he focuses on engine size as the target.

CO₂ emissions are linked also to efficiency and, for example, a sub 1-litre engine will actually consume more and emit more than a modern 1.6 litre turbo diesel. We already have taxes linked to CO₂ emissions, however, this needs to be applied to second hand cars too as we are actually increasing CO₂ emissions through the continued import of second hand cars, some of which, being more than four or five years old will be Euro 4, Euro 3 or even worse while most new cars are clearly already at significantly better levels.

So, rather than increasing tax on high capacity engines, we need to ensure a level playing field that favours cars that have a low CO₂ emission value.