As I understand it the 3p per mile will follow a period of consultation (probably on how to collect it) and will require some solution that has to be in place before eventually introducing it in 2028. Given how well all governments manage consultation and implementation 2028 could well slip.
The reality is that this has been discussed in EV forums for the best part of a decade. It was inevitable that the reduction in fuel duty would leave a hole that needs filling. Pay per mile is by far the fairest version of any duty they could have imposed. A duty on electricity used for EVs would be difficult to enforce, plus public charging is bad enough without sticking an extra 10p per kWh.
I'm Autistic, if I say something you find offensive, please let me know, I can guarantee it was unintentional.
I'll try to give my honest opinion but am always open to learning.
Mark