Yes, we’re letting diesel cars choke our kids. Here’s how we got in this mess

Diesel vehicles are the new enemy, because they’re so bad for the air we breathe. But not so long ago, politicians were urging us to buy them
a car being filled up with diesel at a pump
‘While diesel engines produce less CO2, they do emit other forms of air pollution.’ Photograph: Yui Mok/PA

“You told us to buy diesels!”

These days the average diesel driver is not a happy camper. Hot on the heels of Volkswagens being fitted with a hidden cheat code, we now have the government telling us diesels are not a green choice after all. Sadiq Khan, London’s mayor, is blaming diesel cars for poor air quality in the capital and calling for the older vehicles to be scrapped.

At the same time, the government is still encouraging us to buy diesels. The vehicle excise duty for a car registered after 1 April 2017 is still based on how much carbon dioxide it produces. This tends to push buyers behind the wheel of a diesel, which usually produces less CO2 than an equivalent petrol.

While diesel engines produce less CO2, they do emit other forms of air pollution – especially “sooty particulates”. In layman’s terms, these are unburned bits of tarry nastiness. That is what we are breathing in when we live in a city. Good news and bad news then: diesels are slightly better at saving the planet – or at least killing it more slowly – but they’re choking our kids.

How did we get into this mess? In political terms, it comes down to a difference of opinion between two Labour politicians. More generally, it says a lot about how the public, politicians and experts talk to one another.

For the political history, we need to look back to 1998 when John Prescott published his integrated transport white paper, A New Deal for Everyone. He wanted to use fuel duty to encourage us to buy cleaner fuels. The white paper said: “We are moving towards a fairer treatment of diesel and petrol, based on the energy and carbon content of these fuels. This will mean that the duty on diesel should be higher than on petrol. We began this process in March 1998: duty on diesel is now 1p a litre more than unleaded petrol, and we intend to increase this differential in future years.”

The white paper was pretty clear. The government half-liked diesel because it produced less CO2, and low-sulphur diesel was better than nasty ordinary diesel. But air pollution wasn’t just about CO2. The other pollutants chucked out by diesel meant that, on balance, the tax regime should be pushing people towards petrol. In Prescott’s world, there was a hierarchy of sinfulness. Walking and cycling were very good. Unleaded petrol was slightly better than low-sulphur diesel. Smelly old diesel was the fuel of Satan.

The fuel protests of 2000 and Alistair Darling’s budget of 2009 unpicked all of this. From 2000, the fuel duty rates for petrol and diesel were made the same, and have remained so ever since. In his 2009 budget, Darling replaced the flat rate of vehicle excise duty with rates graduated by CO2.

This reversed Prescott’s idea. Instead of nudging people towards unleaded petrol, the budget of 2009 pushed us towards diesels because of their lower CO2 emissions. Reducing CO2 was seen as more important than tackling air pollution in cities. The government of the day presumably thought that vehicle technology would improve to make diesels cleaner.

Something else was happening. It is something that often happens when a politician has a bright idea about a new policy. Picture the scene in an office somewhere in Whitehall. The minister bursts in to Sir Humphrey’s office in a quiver of excitement.

“I’ve had a great idea,” says the minister. “We’ll reduce carbon dioxide by getting everyone to buy diesels. I was having dinner the other night with a chap from Volkswagen who was telling me all about it.”

Sir Humphrey ums and ahs. “Actually, minister, it’s not quite so simple. On the one hand, diesels are good for reducing CO2. On the other hand, they’re not so good for air pollution in cities.”

The minister laughs. “The public don’t vote for ‘one hand/other hand’ arguments. They want their policies to be simple to understand. The sort of thing you can write on the side of a bus.”

That is where we are today. Politicians and the public like simple policies where any problem can be solved by building a wall, leaving the EU or banning something. But we live in a complicated world that does not lend itself to simple solutions. We lurch from one well-intentioned policy to another as we discover the unexpected consequences of simple soundbite policies.

Sometimes the answer really is “on the one hand … on the other hand …”