With concern about personal finances now at the top of everyone's agenda, it may seem odd to say that British drivers have become eco-warriors – except that ‘eco’ now refers to ‘economy’’ not ‘ecology’.

The proportion of cars sold with emissions under 120g/km (£35 road tax) is rising at an unprecedented rate. Market share has risen by one percentage point every two months so far this year.

It is striking that the growth has been fairly evenly spread across the three segments in which such cars are available: city cars, super-minis and lower-medium models.

Therefore it's not a question of people downsizing into smaller cars to reduce their fuel bills and carbon footprint. Instead, they are looking for variants which offer better figures – for example, the second-best selling sub-120g/km model in July was the Ford Focus TDCI – which isn’t classed as a small car. View our Ford Focus'.

So far this year, the best-selling model in this category has been the Ford Fiesta which, again, is hardly the smallest car you can buy. View our Ford Fiestas.

Underlining the point is the fact that the third-best selling lower-medium model is the Audi A3 1.9 TDIe, which is outselling the sub-120g/km Renault Megane and Citroën C4. View our Audis and our Renaults here.

The message is that eco versions will save buyers on running costs, but that fuel efficiency has an upfront cost.