Fuel duty revenue in the UK is £28billion. That's a big hole to fill.
I suspect that eventually you will be able to charge your electric car only from an approved charger that bills you a higher-rate car tariff, just like you can only use fuel sold at a petrol station in your car.
As for the telematics - excuse me saying so, but the UK government can fuck off with suggesting even more surveillance, it's hard to fight off insurers installing telematics boxes as it is already.
But right now as it stands currently, telematics boxes are nothing else but a greedy attempt to get more cash out of drivers - they collect proprietary data, ran through secret algorithms, to secretly decide whether your insurance should go up or not. Try getting a letter from your insurer telling you that your insurance will go up due to your "driving style" and then ask if they can explain what they mean by that. They can't. "the computer said so" is an absolutely fantastic excuse for these companies to make more money and I'm extremely cynical about it, even if we ignore the entire surveillance aspect for a second. The whole idea needs a lot more regulation/openness to be acceptable.
No idea how to solve that for electric vehicles. Presumably still at the point of charging.