The dash for diesel was the result of lobbying by greens and companies

My Times column on Britain's self-inflicted diesel scandal:

Sadiq Khan, the mayor of London, is right to try to switch the capital away from diesel engines as fast as possible, even if this is tough on those duped into buying diesel cars by years of government incentives and propaganda. Diesel engines do make for worse air quality than petrol engines, and air pollution does almost certainly kill people in significant numbers.

In 2010, the Committee on the Medical Effects of Air Pollutants (Comeap) found that in Britain poor air quality “may have made some contribution to the earlier deaths of up to 200,000 people in 2008, with an average loss of life of about two years per death affected”.

Diesel engines produce more particulates, which damage lungs. Being hotter, they also burn more of the nitrogen in the air to create nitrogen oxides, mainly nitrogen dioxide. Whether nitrogen dioxide is harmful is less certain, but it probably is. Comeap says that “on the balance of probability, nitrogen dioxide itself is responsible for some of the health impact found to be associated with it in epidemiological studies”, rather than simply being a marker for the general impact of traffic on health.

Nonetheless, it is worth getting a bit of perspective. Do you think London’s air quality is better or worse than 20 years ago? I am willing to bet that most people would answer “worse”. They would be wrong. London’s air quality, though bad, has been getting steadily better. The average concentration of particles 10 microns or smaller (known as PM10) is about 20 per cent less than it was 20 years ago and the average concentration of nitrogen dioxide is 30 per cent less.

Going back still further, the coal-smoke pea soupers in the 1950s, the petrol-leak photochemical smogs of Los Angeles in the 1960s, when fuel tanks were far less well sealed, and the leaded petrol fumes of the 1970s were worse. This is not to dismiss today’s complaints: it’s a sign of how high our standards are that air quality is improving, yet we are still unhappy with it. Human beings take progress for granted and demand more of it, as they should.

It is true that the improvement in air quality in London has slowed, even reversing at some roadsides, and that it would have been much faster if diesel had not gone from below 10 per cent to nearly 50 per cent of the new car market over the past ten years. That shift was driven — ironically — by other environmental concerns. In 1993, for example, Peugeot was claiming in adverts that “diesel cars traditionally save fuels, save cash and do their bit to help save the planet”. It was rapped on the knuckles by the Advertising Standards Authority even then.

Minutes of a European Council meeting from 1998, with John Prescott in the chair and Neil Kinnock attending as transport commissioner, emphasised that if the European Union were to meet the targets of the Kyoto treaty on climate change, then emissions of carbon dioxide from transport must start falling. The 1998 agreement between the European Commission and the European Automobile Manufacturers Association (the Acea agreement) was “practically an order to switch to diesel”, according to one observer. Diesel engines, burning hotter, are more efficient and so generate less carbon dioxide for each mile driven than petrol engines, though the gap has been shrinking.

Moreover, a decade later in 2009, diesel was seen as a way to deliver the only mandatory target in the EU Renewable Energy Directive, namely that 10 per cent of final energy consumption in the transport sector should be renewable in 2020. EU subsidies for producing diesel from crops are now about £4 billion a year, and two thirds of rapeseed is used to make diesel. Thus switching to diesel in the name of combatting climate change benefited both German carmakers and French farmers.

By contrast, Japan’s government actively discouraged diesel passenger vehicles from the early 2000s, while American government officials privately expressed astonishment at our diesel dash. A senior American diplomat told a friend of mine in 2009: “Your cities are densely populated, and traffic is heavy and slow moving. Dieselisation will cause a public health problem. Why are you doing this?”

European governments were well aware that in pushing diesel they were risking air quality. Gordon Brown’s budget of 1998 said it “recognises the adverse effect that the use of diesel has on local air quality” even as he shifted incentives towards diesel. Perhaps civil servants were cornered by the logic of their self-inflicted climate targets, and the health problems were regarded as necessary collateral damage; if you have decided to pay almost any financial price to reduce emissions, it follows that practically any other price must also be paid.

Still, there is no point in demonising diesel altogether. World trade depends entirely on giant diesel engines turning the propellers of container ships, with no practical alternatives at present. Similarly, diesels are more or less unavoidable for the road transport of heavy loads. There are some real benefits here. The key problem is urban passenger transport in congested cities such as London. Petrol engines would be better, especially if they switch off automatically at traffic lights, but is the future of urban transport electric? Eventually, yes. Electric vehicles certainly produce less smog, though not none: as traffic increases, a rising proportion of the PM10s in the London air comes from “non-combustion”. This means things such as the smoke of skidding tyres, and dust particles churned up by vehicles.

Because of the battery, electric vehicles are generally heavier for a given vehicle size, and so actually produce slightly more of this stuff. But electrification will take time and cost a lot. Natural gas engines could make a difference sooner. New drilling technologies have made gas abundant and cheap. Cities and towns around the world, including Reading, are running buses on compressed natural gas (CNG), which generates very little nitrogen oxide and virtually no particulates from combustion. The leading countries for natural-gas vehicles are Iran, Pakistan and Argentina, with ten million between them. Delhi started forcing all buses and taxis to use CNG almost 20 years ago, though the huge rise in dirty-diesel trucks has overwhelmed any gains in air quality. It’s scarcely believable that because of EU membership buses and taxis in London still rely almost entirely on diesel.