There is certainly no reason why a vehicle should not run solely on CNG, but, if the supplies are not readily available, it is understandable that many vehicle owners will want dual fuelling. As, during the transition, only a limited amount of CNG would be available, most vehicle owners would demand dual-fuelling facilities.
New petrol-fuelled cars will soon be much cleaner, with the introduction of stringent limits which will reduce noxious emissions by about 80 per cent. compared with the current limits. A petrol engine meeting those new standards would require accurate fuel management and a catalytic converter, but would produce lower noxious emissions than one powered by natural gas without a catalytic converter. There is no fundamental technical reason why cars using natural gas cannot be designed to meet the new emission limits, but clearly any relative percentage differences between fuels will then be of much less importance in absolute terms, as only very low emission levels are permitted.
In the case of heavy-duty engines for lorries and buses, the very low levels of particulates associated with natural gas may prove a useful advantage, but the CO2 advantage in use relative to diesels is lower. Operators of such vehicles are very sensitive to range and cost factors, but in some countries CNG has been used to a limited extent in bus fleets. Some fleet operators may find the special refuelling facilities and operating costs worth while, and the drawbacks of reduced load space and reduction in performance acceptable for their particular operations.
But even in countries where CNG has established a reasonably large presence numerically, the vast proportion of vehicles still use conventional petroleum fuels. On that basis, it is likely that the vast majority of vehicles in the United Kingdom will continue to use petrol and diesel in the medium term. The small proportion of the fleet using natural gas would have a limited benefit in reducing CO2 emissions, but that would not be a complete solution.
My hon. Friend mentioned the desirability of alternative sources of energy. The point is well taken, but we must have regard to practicalities and, with the best will in the world, I do not think that it would be possible at present to convert the whole British vehicle fleet to take CNG, although, if my hon. Friend has his way, it will come about sooner rather than later.