The problem with anything like a per mile tax, or even fuel duty (be that oil or electric), is it doesn't do anything about the two main areas of difficulty; pollution and air quality in inner city areas and congestion. Somebody could travel 3 miles to work and back every day in a city, but that's far worse and more harmful than someone doing 25 in the country.
I think we're already on the right lines: grants for EVs, emissions-based tax and 'tolls' so-to-speak like London's ULEZ. They just need to go further, but it has to be a gradual process - you can't just overnight ban non-low emission vehicles, it has to be a gradual change in-line with uptake, infrastructure, physological adoption etc.
I wrote to Bristol's mayor because I was really peeved off that someone from TravelWest who was supposed to be promoting EVs said that the council were clamping down on people charging their vehicles on-street and were issuing fines (despite I would guess 95%+ of the homes within the planned low emission/diesel ban zone not having driveways) and to be fair he did respond pretty positively, namely:
Thank you for writing, and for your positive comments on our Clean Air Zone plans. We have a moral, ecological and legal duty to clean up Bristol’s air, and I am confident that these plans will help us reach legal compliance for air quality in the shortest possible time while protecting those on low incomes.
I am copying in my cabinet member for Transport and Energy, Cllr Kye Dudd who can respond in more detail to your suggestions about EV charging infrastructure. We want to encourage citizens and businesses to transition to low emissions vehicles wherever possible. Bristol City Council have no plans that I am aware of to clamp down on the installation of charging points in homes without driveways.
We recognise that expanding our charging infrastructure is a key step in making our city carbon neutral by 2030, and have identified this is an area for the whole city to collaborate on in our One City Plan.
As someone earlier said, nobody is going to know there's demand for charging points, or localised barriers to EV uptake, unless you tell them. Bristol seem to be doing an ok-job, they're building dedicated charging hubs and you can request/view planned locations for individual public chargers at
http://bcc.maps.arcgis.com/apps/webappviewer/index.html?id=c65b68b9282e43e994130b5f591c685e. I've already requested 3 on and adjacent to the road I live on which now show as under investigation.