Thanks everyone. I've been using an external hard drive. I know I should pop it in the safe, but confess idleness precludes this - (the safe's half a mile away)
Keef's batch file system has appeal. However, I would despair of trying to automate backups on Mrs JTR's machine: she has the habit of dropping files into random places (cf the 'flat surfaces' thread in JB) and then telling me I've hidden them.
As if.