Straight off, I have read a lot of, but not all of, the posts in this thread, so there is a risk of repeating the points others have made.

To the people that have fears for their situation, it looks to me like the answer is clear, but it may not be palatable. There are 2 options:

1) scrap the car, get "end of life" documentation and be prepared to address possible penalties for historical discrepancies.
2) do not scrap the car and continue to risk exposure to historical and additional future penalties as time goes by.

I have sympathy for those that have inadvertently and through no real fault of their own ended up with cars that they are going to get hung out on.

However those are relatively few and, I'm afraid I don't have a great deal of sympathy for those that are simply getting caught out, knowing that their cars were inappropriately classified. I seem to recall discussion threads on predecessors to this forum where those that weren't evading appropriate levels of road tax were being called mugs.

The bottom line is, tax evasion has always been an offence, whether it be road tax, income tax, or other.