Is it the UK or EU leading the emissions thing thus affecting diesel sales which is probably a major factor in this? Or is it something else?
The regulations (ie the new wltp cycle and eu6 emission limits, plus crash standards and others) are set by the unece group, in which the eu nations effectively have a casting vote, however any car sold must meet these standards (gasoline or diesel).
The “demonisation” of diesel is very much on the shoulders of individual gouvernements, none of whom actually have any semblance of understanding about combustion chemistry. Mazda have recently productionised one of the automotive holy grails - a compression ignition gasoline engine (ie a petrol engine that works like a Diesel engine without spark plugs). This engine will be great for CO2 / fuel economy, but very poor for hydrocarbon particulates - one of the main pollutants that had lead to the demonisation of diesel.
In a Diesel engine, the best way to lower CO2 (as regulators have been pushing automotive OEMs to do for years) is to run them lean (with an excess of oxygen) which gives a really nice clean aggressive burn. Unfortunately this also gives very high in cylinder temperatures, which leads to much higher NOx. You resolve this by putting filters (DPFs) in the exhaust, which increase back pressure and reduce fuel economy.
I worked for JLR until 6 months ago, and I’m certainly glad I got out when I did.
I now work for another automotive OEM who make 5.2l V12s that are likely to be fully legal to drive into inner cities when small, relatively modern diesels get banned.
Who’d be an automotive engineer...