How do they intend to enforce/track/manage it?
If they do it via yearly MOT, people will start clocking cars again. If they go for a blackbox, then the costs are epic and I've no doubt a faraday cage would limit a blackbox.
It's difficult to implement those style of recording without doing it at the manufacturing stage.
The fairest way is to put it on fuel, but they wouldn't just add 2p, they'd add a lot more. I've said this for years, do away with road tax, add a penny to each litre of fuel and you'd get about the same amount, but with the added benefit of those who drive more, pay more and those who avoid paying to use a car, will still get stung for road tax equivalent at the pump. It would also save millions in being able to get rid of a large section of the DVLA. Sadly I don't trust any government to implement this in a sensible way, they are too greedy.