Smart meters and smart chargers could be used to identify when EVs are being charged and hence attract a higher tariff accordingly. The road footprint of EVs is the same as ICE vehicles in respect of congestion, and by most accounts total lifetime environmental impact of EVs is not much different once manufacture and scrappage are also included in the equation. And if the aim is to reduce personal vehicle travel generally, the tax revenue gap will still need to be plugged - higher taxes on other forms of travel perhaps? Such as diesels running under the wires...
With rail there needs to be a balance, as even with the high emissions from diesel trains the overall railway emissions are comparable to that of EV's on a per passenger per km basis.
Whilst that doesn't mean that we should accept diesel trains long term, we're probably talking about at least 5 years out before milage charges are likely to exist and hopefully there'll be some noticeable reductions in diesel use in that timeframe (not least the Avanti replacements for the 221's and the EMR replacement of the 222's and extra electric rolling stock). If we could get a bit more electrification as well, then all the better.
If we're trying to plug the gap then chances are air travel will also see extra charges.
However as I've already highlighted where overall milage is likely to fall due to WFH or could start to get difficult to match previous years tax incomes.
I suspect that the start of milage charging could be applied to all vehicles at a fairly low rate (2p per mile) and as ICE use falls the rate increases to offset the loss of fuel duty.
It would ensure that EV's were always the cheapest way to get about, but the costs would grow slowly (for example growing from an average of 2p in 2025, then increasing 1p per mile per year to 7p in 2030 and then increasing 1.5p per year to 15.5p in 2035) so that the impact on use wouldn't be so great.
If it costs you £200, £300, £400, £500, £600, £700 £950, £1,100, £1,250, £1,400 and £1,500 then for each year you may well be inclined to reduce your use a little and be more willing to switch from an ICE to EV (especially if fuel duty starts to rise again too) however each extra increase isn't so much that it's likely to cause significant impact to most people.
In reality chances are for most who can swap to an EV there'll be some years where they make significant savings over the current costs for using an ICE.