But Honda recognises that the petrol engine is with us for many years yet, and therefore needs to be constantly updated and refined to improve air quality in the world's burgeoning cities, particularly in developing countries.

To this end, Honda has developed three levels of low-emission petrol engine technology, which it is introducing progressively. These are:

· LEV (Low Emission Vehicle) - a production-ready standard now being introduced; outs toxic emissions by more than 80 per cent from current government standards.

· ULEV (Ultra Low Emissions Vehicle) - cuts smog gas emissions by a further 90 per cent; being trialled in the United States.

· ZLEV (Near-Zero Low Emissions Vehicle) - an experimental technology that promises to reduce emissions of the three smog gases (carbon monoxide, hydro carbons and oxides of nitrogen) to just 10 per cent of ULEV levels, or near zero.