That's the wrong way to look at it. How much would it cost to fuel a car in petrol per mile? You are still making a massive saving.
The other issue is that in fuel duty the govt bring in £billions each year, as we migrate away from petrol cars that money needs to come from somewhere so it was pretty obvious this had to be introduced at some time.
Also, as you use the roads and your car is heavier surely you should contribute a bit. Your road tax is also lower than a standard car.
It is also not being introduced for a few years.