Thanks mb, that's definitely got me going in the right direction, unfortunately there are are two dependencies that can't be resolved:
No matter what I try I can't get them installed. (And someone somewhere should be shot for writing such a useless and uninformative message: "it is not installable"....)
Depends: mate-conf but it is not installable
Depends: mate-conf-common but it is not installable
Apt-get is slightly more helpful:
But I can't find out what to do about this, no matter how much I google it....what can I do about this?
E: Package 'mate-conf-common' has no installation candidate