Gwen and Ian I am so sorry for not replying to this! I don't recall ever seeing a notification that you had replied.
Our provider did manage to switch this off but a recent upgrade has undone this and our providers don't seem to be able to switch this off. Even more frustrating is the fact that the Outlook calendar events are being sent out an hour out of time! Very confusing for our users and is apparently a global Moodle issue....??