[chris]

there was what, at least appeared to be, actual visible smog at the time

When you fly into Johannesburg in the morning the plane passes through a layer of brown air hovering over the city...

[wolfekeeper (OP)]

Apparently there's over a million vehicles in the UK with the emissions software on it.

If the car is pumping out, on average, 5 times the emissions it should then it's presumably around 1/7 of the UK NOx emissions from the 35 million cars, if everyone else is telling the truth about their emissions.