I'm not sure there's a good solution.
Assuming we could trust the Government (which, BTW, I don't believe), the first thing we should do is put the "road tax" on petrol and abolish the tax disk. Then we could have default third party insurance paid for again with a tax on petrol. I believe this is the system they have in New Zealand. That just leaves us with the problem of a roadworthiness inspection (aka MOT). I'm not sure how to deal with this, without ending up with disks and whanot, in which case we're back where we started only now with extra taxes on petrol (which is what I believe happened in Ireland; they abolished the tax disk and put the tax on petrol. Then had an admin fee for checking documents each year, which crept up until it was the same as the road tax had previously been, so now they're back where they started only with two taxes instead of one.)