Last month, more people bought diesel cars (or, rather more accurately, more diesel cars were registered) than in any previous September.

Okay, they made up a slightly smaller proportion of new car sales than usual, but that’s not surprising. Firstly, because there’s a natural trend towards ever more efficient petrol engines and alternative fuels, and secondly, because some diesels have been getting a tough time of it recently. I don’t know. You might have heard.

Anyway, still encompassing nearly half of all new car sales, diesel is not really going anywhere. And in towns, lots of diesel cars not going anywhere is precisely the problem.

Diesels have been made popular because they will often emit less CO2 than a petrol equivalent – which is better for not warming the planet – but they’re worse for you if you live in an urban area, because they upset the local air quality by putting out more mono-nitrogen oxides and particulates. What’s good (or less bad) for Arctic tundra is bad for Mrs Miggins of Kilburn High Road, and vice versa.