[Adrian E]

When Gordon Brown incentivised diesels, through company car tax based on CO2 emissions, diesel was traditionally a cheaper fuel to buy due to lower demand. At the time the ozone layer and greenhouse has emissions were what environmentalists were worried about.

Fast forward a decade and the fruits of that decision, plus a good deal of scientific research into the effects of breathing particulate and oxides of nitrogen means we now understand how damaging to long term health this stuff really is (the smaller it is, the deeper into the lungs it gets.....and it never comes out)

Add in that vehicles, petrol or diesel, have always been designed to pass whatever test regime exists at the time of type approval, and in the real world have generally put out considerably more emissions (both CO2 and air quality related) and it's clear that whatever fuel is flavour of the month/year/decade is going to result in some shift in the proportion and type of tailpipe emissions.

I recall buying our petrol C5 A6 around the time the higher band tax rate came in (based on CO2!) which knocked £3-4k off the value overnight.

The treasury set fuel duty with little to no regard for policy incentives around emissions - they look at a macro level of 'how big a pot will we create based on z/y/z scenario, and what levers do we have to pull'. Look at the over £40k 'high value' VED and £140 flat rate as an example of that - took away the incentives for EVs in VED terms, but re-inflates the coffers when less and less people are paying the traditional few hundred quid a year for the privilege of parking their car on the street.

Basically drive your (presumably 'clean' with fully functional DPFs) diesel on the motorway, happy that it is the right vehicle for the right use. Don't drive it in town, where it's creating pollution where it has the most impact at low level with pedestrians around, or expect to be gradually forced not to by changes in local measures that make it too expensive to do so. Or just pay up and work on the basis there is certainty in live, death and taxes!