Enough hysteria, already. Sure, it’s shocking, knowing bosses at Volkswagen used naked, unprincipled, indefensible skulduggery to get their cars past American emissions standards that honest rivals found almost impossible to achieve.

But now, downstream of the revelations, I reckon it’s time for a bit of calm. The key controversy is over emissions of NOx from car exhausts, about 40% of which emanates from all transport sources, and half of that from cars. The crooked VWs are thus responsible for a slice of 20%, so even if they could be rendered legal overnight, we’d still have a problem.

For decades we’ve been directed by academics and government agencies to care most about reducing CO2 on the grounds that it’s a greenhouse gas that contributes to global warming. Diesels emit less CO2 than petrol engines (good) but much more NOx (bad), and the latter is now accepted as a serious health hazard. Things must change.