Ah yeah. No point speculating on that so far out. We'll be through at least 2 more GE's by then, and this is something that governments love to tinker with.
If it was me in government, I'd be approaching it by gradually bringing EV annual "road tax" up from the current "incentive" low levels while at the same time ramping up ICE road tax even faster, especially for the biggest and heaviest polluters. As part of that, I'd look at doing away with the "what the road tax was on the day the car was bought is what it will be permanently" for ICE vehicles and replace it with a system with the road tax scales upwards with vehicle age (possibly linked to a new yearly MOT additional test that tests emissions and the amount the tax increases is linked to the tailpipe emissions at that test - which would also incentivise drivers to maintain their ICE properly if they're going to keep it).
