Leading Article: For drivers with a green conscience

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NOISY, dirty and uncomfortable, the diesel car was once seen in Britain as the automotive equivalent of French plumbing. It has taken tens of millions of pounds of research and development and advertising for car manufacturers such as Peugeot, Fiat and Volkswagen to change that view. But no sooner have they established their brainchild as fashionable, environmentally friendly and economical, than a group of government experts produces a report saying that diesel is far less green than petrol.

Drivers who are attracted to diesel because they want to save money should not be put off. Although in Britain it is now no cheaper than unleaded petrol, modern diesel cars can be nearly as refined as their petrol equivalents, and much more economical. One large fleet owner has discovered that its diesel cars use 37 per cent less fuel; city drivers may find the figure nearer 25 per cent, but still a useful saving.

The harder question is whether diesel can still claim to be the environmentalist's choice. Because they use less fuel overall, diesel engines pump out less carbon dioxide, carbon monoxide and hydrocarbons than today's clean petrol engines, and therefore contribute less to global warming. But the drawbacks identified by the Government's Quality of Urban Air Review Group are serious. The group's scientists concluded that diesels are much worse than petrol engines in poisoning cities with oxides of nitrogen (which contribute to acid rain and smog) and with tiny particles of cancer-causing, asthma-aggravating soot.

The diesel brigade is confident that a few years' more R & D will allow it to overcome these problems. That does not help the green- minded would-be buyers of diesel cars now. The moral for the truly conscientious motorist might be to opt for a small, petrol-driven car for now and wait until further development swings the balance in favour of diesel.

The Government, for its part, should resist calls to follow France's lead in subsidising diesel fuel with lower taxes. If it wishes to save the planet and make life more pleasant for city-dwellers, it should take the less controversial step of tightening the emissions check which is already part of the MoT test and consider new legislation to take grossly polluting vehicles immediately off the roads.