This is all to do with emission levels. There are 'Euro' standards that must be met by ALL vehicles NOT just diesels
http://www.autoexpress.co.uk/car-news/consumer-news/90816/euro-6-emissions-standards-what-do-they-mean-for-you
The current standard is Euro6 which ALL vehicles sold since the start of 2015 MUST comply with.
For diesel engines Euro6 includes particulate filters and Adblue technology and as well as catalytic converters.
The catalytic converter burns Carbon Monoxide,which is poisonous to Carbon Dioxide which is not . The particulate filter removes the fine particles and automatically burns them off when it is full.
Adblue removes NOX from the exhaust.
Any diesel that meets EURO6 will NOT be affected by any ban or surcharge and will NOT qualify for the scrappage scheme even if it is introduced.
The idea is that eventually there will only be Euro6 and above vehicles on the road. Euro7 will soon be introduced which has even lower emission levels than Euro6 . Euro8 is further down the line!
I have a Vauxhall Zafira 7 seater with a Euro6 ecodiesel engine.
It does over 45 mpg around town and well over 60 mpg on a long run! No petrol car of the same size can come near that!
By the way 'Euro' emission standards will NOT be changed once we leave the EU!