Re: It's not just diesels
"I have long said that the pollution levels in London, for example, prove withoud doubt that large diesel engines, in this case, buses, emmit SEVERAL times the max ammount of NOx permitted, as streets with only buses demonstrate. No doubt about it."
You'd be wrong though. In 2009, only 60% of NOX in London was generated by vheicles. The rest came from stationay sources - almost entirely 1970s era boilers with unsealed flues. These also emit copious quantities of carbon monoxide and inspectors could identify individual properties thanks to the scale of the emissions - only 40,50,000 boilers are responsible for at least 90% of the stationary-source NOX in London.
The relevance to vehicles is that even with cheating, Euro5 and 6 did reduce real-world emissions and that, along with retirement of older vehicles and the "clean air zones" means that vehicle-sourced NOX is well down on what it was in 2009 and non-vehicular NOX is something over 60% of the total of what's left.
Boiler emissions have been regulated since 2003 - and NOX was why councils were pushing condensing systems hard before this (condensing boilers emit almost zero NOX as it's absorbed into the water), however _existing_ systems are grandfathered against enforcement for around 20 years.
Most owners of these boilers have been approached and informed how polluting their installations are and offers have been made to assist in upgrading, however they generallly refuse point blank to do so and will stay refusniks until legally compelled to do so. Almost all of the offenders are wealthy individuals who can trivially replace their boiler installation. Money is not the issue and there are hints that attempts to force the issue will be strongly resisted in the courts when the NOX exemptions are removed.
Of course _who_ these people are is confidential data and can't be leaked. Being named and shamed might be a motivator but it's not a tactic that can be used, especially when the polluters have political clout and money.