Geektastic:
Surely the idea is to encourage people not to buy high emission vehicles? Once that happens (and it’s not hard - my Mercedes E400d has a 3 litre twin turbo straight six diesel and it attracts no penalty) it won’t be cost neutral.
The number of vehicles that receive a fee increases each year as the emission limit is lowered. So each year, more new ICE vehicles will be contributing to the fund. As the scheme gets further down the line then less vehicle categories qualify for the rebate (ie, efficient ICE vehicles are removed, hybrids, PHEVs, etc) and the rebate value starts to reduce.