A flat "per mile" is a bad way to measure road consumption for a vehicle. The more accurate measure is weight of the vehicle+mileage. A heavier vehicle will do more damage to roads. There is at least some correlation on petrol/diesel because a larger vehicle will have to consume more fuel to move a heavier vehicle.

However, if there is a flat 3p tax per mile irrespective of the weight of the vehicle, then smaller/lighter EVs will be paying disproportionately more of the cost of road damage than larger EVs.

The only fair road/gas tax is to charge all vehicles (not just EVs) per mile using a formula based on mileage and vehicle weight. This includes buses and semi trucks.

Electric vehicle odometers can be tampered with using specialized equipment, so taxing based on mileage would be inapplicable if the fees were excessive. Currently, China has the most developed electric vehicle market, yet it has not yet resolved the issue of electric vehicle taxation, which is worth considering.