News on Monday morning that Ford is spending £190 million to expand Dagenham production of 2.0-litre turbodiesels for use in both vans and cars – and has won an £8.9 million grant from the government’s Regional Growth Fund into the bargain – makes certain elements of both the daily media and the political classes look rather silly. And confuses many people.

For many weekends recently, the Sunday papers have published stories from academic research sources to the effect that the decades of encouragement we’ve had to buy diesel cars – mainly because, on balance, they’re cleaner – is completely wrong.

The combination of exhaust particulates and oxides of nitrogen they emit, not well enough measured in current official tests, is allegedly killing both us and our children. London mayor Boris Johnson has been vocal about the damage being done by diesels – yet David Cameron and Vince Cable deal out financial incentives to encourage further production, in outer London, regardless. 

What’s the truth, then? The overall situation is simple, but poorly explained. The official tests are indeed inadequate. They need urgent overhaul to better measure particulates and nitrogen oxides, and in typical, not laboratory use.

Equally, the activists need to acknowledge that the problem is on its way to being defeated: the Euro 6 standards that latest diesels are required to meet by September but many meet now – admittedly measured in the old way – are already clean enough to pass the standards Boris has in mind for his 2017 ultra low-emission zone.

The Euro 6 standards are particularly strict on especially on particulates and NOx, though neither the mayor’s people nor the activists seem inclined to acknowledge the progress.

The desirable situation, as usual, sits between extremes. The tests need revision, and soon. Those with diesels with exhaust standards below Euro 6 need to keep them out of polluted and congested areas — preparatory to swapping them as soon as possible for something cleaner.

And by the way, Boris and company could bite the bullet and rid the metropolis of the many ancient taxi diesels they still allow to ply our inner city, individually pumping out more exhaust rubbish than any other 20 cars of the past decade. Why they’re still allowed is beyond us all.