To ask the Secretary of State for Transport what estimates he has of the effects of the fitting of catalytic converters to vehicles in terms of noxious emissions, other emissions and fuel consumption.

On the basis of road tests carried out by the Government's Warren Spring laboratory, a typical vehicle equipped with a catalyst in good condition will reduce its emissions of carbon monoxide, hydrocarbons and oxides of nitrogen by approximately 90 per cent. in each case. On the other hand, fuel consumption will increase by 3 to 9 per cent., and there will be an increase of 9 to 23 per cent. in carbon dioxide emissions.