None of the examples in the docker help seem to work but I found a strange setup that does wok, I used the following command
docker run --name ubuntu-run -it -v //c/Users/Selvyn/demo/vm_share:/var/lib/host.demo ubuntu
The key seems to be in the //c/Users/Selvyn which is C:\Users\Selvyn. This can be mounted, but anything outside of C:\Users\Selvyn won't work??? I suspect it is something to do with privileges.