"A would disagree that EVs are subsidised because while petrol is taxed, the environmental impact is not factored in."
Governments tax to obtain money. Some of that is even spent on building and maintaining roads, not that that's always immediately obvious. Governments could claim green credentials by exemptions for EVs but only because the fleet was small enough for the tax not taken to be counted as small change in relation to the rest of road taxation. As soon as the loss of taxation becomes significant then it has to be made up somehow, either by taxing something else or by bringing taxation on EVs into line with other vehicles.
Couldn't happen? It happened to diesel a few years ago; there are still people complaining that they were suckered into buying a diesel car because the fuel was less heavily taxed and now they're paying more.