It will not take too much especially for more modern cars with greater electronic and emission control systems to be forced off the road by eg manufacturers instructed not to hold stocks for cars say not say Euro 6 compliant or for the MOT emissions testing to be come more demanding and failing cars not meeting original emissions standards when new, especially with the widespread cheating that went on by most vehicle manufacturers in recent years to achieve lower emissions.
Doesn't take too much to clear the roads of ICE, eg force the fitment of catalytic convertors to older pre 1992 vehicles to clean up their emissions, so many ways to go about it.
