I am fairly experienced but far from expert.
I have been concerned about shadow copies for a while, and as far as I can see, they should be deleted if I delete the system restore points. This, of course would leave everything since the last one still insecure so I have been creating a new on, and then deleting the old. Finally wiping the free space.
I am now wondering if this actually works, and would appreciate it if anyone could either reassure me, or advise me of a better method.