You guessed wrong! What dinosaur juice makes the electricity for your car?

Renewable energy is still only 40% of UK consumption.
The environmental argument here is an indirect one.
When all private vehicles are powered by electricity, it will be possible to swap the energy production method - in future - seamlessly in the background.
This is important, because if you look at the history of similar issues, environmental modifications to ICE cars can take decades to complete, with older 'non compliant' cars lingering on forever - just look at what happned things like getting rid of leaded petrol, or getting rid of polluting pre-EU6 Diesels.
This is because at current, each private ICE car is a small portable energy plant. The transition from ICE to electrical propulsion turns the car into an electric consumer instead, and moves the energy production to a much smaller number of locations where the electricity is produced centrally then distributed to the cars via the grid.
The move from local energy production to centrlised energy production for private vehicles has several benefits:
Firstly, as said, swapping to greener energy sources in future will be far easier and quicker. The counter argument, by the way, is that this is a bit like Cryonics - we don't have a cure, so we're freezing the problem in the hope that a cure will be found one day.
Then, emissions can be much better controlled and manged in national power plants than in motor vehicles' engines, even with the expensive and elaborate after-treatment systems.
And last, as I keep mentioning, centrally produced energy moves harmful exhaust emissions away from densely populated areas which is where most people live and work.
But, ultimately.... we just need to have less cars, and drive them less. That's the key for 'saving the planet'.