Yes I suppose the Brexit comment sounds more like a failed joke now that the car companies are leaving but I think a widespread deregulation may follow as they already scrap basic human rights that they do not want to pass to the new laws. It is a wait and see game but if any car manufacturer stays behind, they will produce EU compliant cars to sell them to Europe, so the local law will somehow approve them. It seems very difficult to believe that the public will start buying brand new Russian/Chinese/Other similar new old cars that are based on past regulations after they got used to cheap finance and niche models, but somehow the government argues that this what they people want to do.
Maybe the car tax increase will do the trick as well. But I think this works only for the most expensive £500+ tax. There were cars like the Daewoo Tacuma that suddendly got a £500 per year tax and people started selling them for nothing. But even that is something like £10 per week like buying a meal deal insteading of cooking at home once per week. So some people will still keep the cars they like.
I think the previous tax system made sense considering the consumption was increasing the emissions and therefore there was more fuel burnt. But even with that, gradually I think people saved very little by buying a newer model because of the huge depreciation.
The current flat rate is like the government admitting that only cared about the money that could charge. They already make plans on how to make up a new tax system for charging electricity. Currently the fuel is taxed at 58% and they add 20% to that and the VED. Then you can fly around paying no duty or tax, stange times.